SVOM

The SVOM satellite and the ground/space-based strategy

The advent of space faring in the 1960s undoubtedly opened a new era in the exploration of the Universe. Access to space now allowed scientists to study radiation that was impossible to measure from the ground and to benefit from special observing conditions, such as the absence of atmospheric turbulence.
Nevertheless, the complementarity of ground and space-based observations quickly became a necessity owing to the need for multi-wavelength coverage of celestial targets. Today, any space project must include a ground-based component in its preparation and support from terrestrial observatories for follow-up observations. The implementation of synergized ground and space-based observations is however subject to several types of constraints imposed by the mode of operation of the satellite and the nature of the ground-based operations.
SVOM is a low earth orbit satellite, orbiting at 650 km. At this altitude, the satellite travels around the Earth in just over 95 minutes (15 revolutions per day). The orbit is inclined by 30° with respect to the terrestrial equatorial plane and as a result, the satellite’s trajectory oscillates between latitudes of +30° and -30°. The orbit parameters are the result of a compromise between the launch site, the power of the launcher (and its cost) and the satellite’s stabilization system. The video below shows the track of the satellite (in green) over several revolutions; We also distinguish the day zone and the night zone, credit: CNES.

The first constraint related to the low earth orbit is to ensure permanent contact with the satellite. One solution is to deploy a network of antennas under its track. The choice of the satellite’s inclination then fixes the number of stations. In the case of SVOM and its 30° inclination, this means appropriately distributing 47 antennas between latitudes -30° and +30°.
The second constraint is imposed by the need to maintain the satellite and its instruments at suitable temperatures. One solution consists in defining a cold face of the satellite so as to evacuate via heaters the calories produced by the electronics. This cold face must be maintained at more than 90 degrees from the Sun. As a result, half the sky is not observable at any given time.
The third constraint linked to the scientific objective of the SVOM mission is to always observe areas of the sky accessible by ground telescopes during their local nighttime. This implies that the optical axis of the instruments on board the satellite point in the direction opposite to the Sun. This strategy comes at a price however: the Earth will hide the field of view of the instruments once per orbit, up to 50% of the period of revolution i.e. 45 minutes.
The fourth constraint is determined by the vital access to large ground-based telescopes (VLT, Hawaii, La Palma). In order to benefit from optimal observations, the area of the sky targeted by the onboard instruments must be close to the zenith of these large telescopes.

Other constraints are imposed by our galaxy: the Milky Way. Indeed, our galaxy harbors many transient X and gamma-ray sources able to mimic a burst and to trigger the detection chain. Furthermore, if a burst is detected through the Galaxy, its ground follow-up will be strongly affected by interstellar absorption. Finally, the Scorpius X-1 source located outside of the galactic plane is extremely bright in the energy range studied by SVOM. In order not to disturb the measurements, it must be avoided.

These strongly coupled constraints led to the definition of the cold face of the satellite, the arrangement of the onboard instruments and the pointing strategy. The latter is commonly referred to as the « attitude law ».

The Ground/Space Synergy

The study of astronomical objects requires many resources, in particular from a material point of view. It is necessary to be able to acquire the most precise data possible, all the while launching a satellite with the flexibility of execution required for the observation of transient phenomena. The key word is optimization. To best meet the mission’s objectives, the synergy between the onboard instruments and those present on Earth is crucial.

SVOM thus implements an appealing combination of instruments.

Step 1: Detect and Locate
Detection takes place in space because gamma rays are stopped by Earth’s atmosphere. This task is devoted to the ECLAIR telescope, whose detection rate is estimated to be about 80 per year, with approximately 20% of very distant events with redshift greater than 6.An estimate of the event’s position in the sky is then transmitted in a few tens of seconds to the scientific community, transiting through the VHF alert network, whose relay antennas are strewn along the intertropical zone.

Step 2: Observe the Prompt Emission
During the time taken to localize the burst, the GRM gamma monitor will be able to provide an estimate of the peak energy (Epeak) of the burst. The peak energy is defined as the energy at which the burst radiates the maximum energy. Several studies seem to indicate a correlation between Epeak and the absolute brightness of the burst. On Earth, the GWAC, wide-angle telescopes, will give an observation of the prompt emission in the visible field.

Step 3: Increase Location Accuracy to Enable Follow-up
After the satellite’s automatic slewing maneuver in less than 5 minutes, the MXT and the VT, supplemented by the two GFTs on the ground, will ensure multi-wavelength follow-up systematically for several hours. (The VT will in particular allow the detection of nearly 75% of gamma-ray bursts in the visible domain, and for the first time, explore the area of dark bursts, for which the optical counterpart is not detected.) This marks the beginning of the search for afterglows.

Step 4: Redistribute the Alert
All these instruments are part of a cascade of operations designed to refine the location of the burst from a few arc minutes to a few arc seconds. The alerts will then be redistributed to the scientific community in real time through the GCN alert network or other networks available at launch.

Step 5: Determine the Distance
In the event of a good position estimate, the large ground-based general-purpose telescopes with a smaller field of view (such as the ESO VLT in Chile) will provide the possibility to acquire a spectrum. It will then be possible to measure the redshift in order to estimate the distance to the source.

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Author : CEA/Irfu

What is a gamma-ray burst ?

Manifestation of a gigantic explosion, these flashes of light are considered to be the brightest and most energy-rich events since the Big Bang.

Un sursaut gamma s’accompagne d’un dégagement de matière sous forme de deux cônes opposés. https://www.eso.org/public/france/images/eso0917a/

A gamma-ray burst is accompanied by a release of material in the form of two opposite cones. Credit: ESO

These are rare events on the scale of a galaxy, yet it would be possible to observe on average ten per day.
The power that emerges is considerable, the equivalent of more than a billion billion suns. This makes them visible at very large distances, even beyond our galaxy. However, their detection is difficult and real technical prowess is needed to observe the random and unpredictable gamma-ray bursts.

A rush of gamma photons

These explosions are called « gamma-ray » in reference to the particles of very high energy initially released: gamma photons. Just like visible light, X-rays or radio waves, these are  electromagnetic waves.

Les rayons gamma (?) sont les ondes de plus petites longueurs d’onde (?) du spectre élecromagnétique. Le spectre de la lumière visible, à titre indicatif, est représenté par les couleurs selon la longueur d’onde croissante.

Gamma rays are the electromagnetic waves with the smallest wavelengths in the electromagnetic spectrum. The spectrum of visible light, as an indication, is represented by the colors.

The energy of a photon is measured in electron-volt (eV), a photon of visible light emits about 2eV. That of a gamma photon can reach several billions of electrons-volts!

Birth of a gamma ray burst

The explosion at the origin of the burst fulfills specific conditions. Today two scenarios explain the power and rapid variation of gamma ray bursts: the coalescence or fusion of two compact objects (neutron star or black hole) and the collapse of a very massive star.
The majority of gamma ray bursts recorded today indicate that they appear during the death of a very massive star. Indeed, under the scenario of the collapse of a star at the end its life, this one must be very massive to provide the energy required for the ejection of matter at very high speed. It is this material, when propagated in the surrounding environment, that will allow the transformation of this energy into gamma radiation.
At the moment of the explosion, we can distinguish several stages explaining the appearance of the burst, according to the so-called « fireball » model:

Illustration du modèle de la boule de feu. Crédits : NASA

Illustration of the fireball model. Credit : NASA

  1. The progenitor produces jets of material consisting essentially of packets of electrons, ejected in sporadically in a particular direction. These packets are expelled at different speeds but all close to the speed of light. These jets are therefore said to be ultra-relativistic.
  2. Very violent shocks take place when these packets of electrons come into contact with each other: it is the model of the internal shocks. The layers of material expelled at different speeds end up colliding, the fastest layers catching up with the slowest. These shock fronts will abruptly generate gamma rays. This is called the prompt emission.
  3. There are also external shocks where these same layers of matter interact later with the surrounding environment of the progenitor. This gives rise to less intense, less energetic radiation, which is spread out over time and composed of X-rays, visible light and radio waves. This is called the afterglow emission.

The conditions of appearance

The duration of the burst indicates two possible origins:
When the duration is less than 2 seconds, the burst is called a short burst. It would come from the coalescence of two massive and compact objects such as two neutron stars, or a neutron star and a black hole.
These two stars, in orbit, end up « falling » on each other as they lose energy by the emission of gravitational waves. From this ultimate encounter a new black hole is born.
In the case of long bursts, those lasting more than 2 seconds, they are produced at the end of a hypernova, a type of supernova. A hypernova is a star whose mass is greater than 20 times that of the sun and which undergoes gravitational collapse. A black hole is created abruptly causing shock waves that explode the rest of the star and pierce the stellar envelope: the outer layers are violently expelled. This is called the fireball model.
In both cases,  the newly-formed compact object (probably a black hole) grows swallowing  the matter in its immediate surroundings in a matter of seconds and forms a thick, rapidly rotating accretion disk arond itself. A part of the matter attracted by the gravitational force of the black hole is expelled in the form of two opposing jets along the axis of rotation of the disc following a physical mechanism still far from being understood.
This ejection at very high speed generates the shocks previously described and reveals the gamma-ray burst, as a result of internal shocks. In order to perceive its light, the observer must therefore be aligned with the axis of emission.

The afterglow emission

The afterglow emission of a gamma-ray burst is the phase which follows the prompt emission. According to the fireball model, it is due to shocks which during their expansion will sweep the environment surrounding the progenitor, generating radiation at all wavelengths. Its study thus makes it possible to know the nature of the environment of the progenitor. The remanent emission is not as brief as the prompt emission. It gradually decreases on a timescale of hours, days or months. This makes it possible to carry out observing programs with ground or space telescopes, provided that there is a sufficiently precise position of the burst, in particular in the X-rays and in visible light. The information provided by the afterglow emission is crucial for a better understanding of the explosive phenomenon and the environment of gamma-ray burst progenitors.

The fading image of the optical afterglow of GRB 030329, as seen on April 3 (four days after the GRB event) and May 1, 2003. The images were obtained with the FORS 1 and 2 multi-mode instruments at the 8.2-m VLT telescopes.

On the left, image obtained on April 3, 2003 of the afterglow emission in optical of the burst appeared on March 29, 2003. Right, a month later, the emission is always visible but weaker because it decreases gradually. Credit: ESO

Nomenclature

GRB for Gamma Ray Burst, followed by detection date, yymmdd.
Example: GRB 970508 corresponds to a burst detected on the 8th of May 1997.

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Author : CEA / Irfu & Jesse Palmerio

The transient sky

Variable and transient bodies have played a major role in astronomy for a long time, as shown by the observations of Chinese astronomers reported 4000 years ago (see the article). Comets, novae, variable stars, supernovae, gamma bursts or coalescence of compact objects causing the emission of gravitational waves are among the objects of this variable and transient sky, far from the classical representation of an unchangeable, static sky.
The rise and the interest in observing the transient sky are closely linked to the technological developments and progress of detection tools: more sensitive sensors, therefore shorter exposure times, access to new wavelength domains, increased power of storage and data processing resources, the advent of wide-field cameras mounted on increasingly large telescopes, their effectiveness and interaction with alerts given by the instruments developed in the field of non-magnetic messengers.

Variable and transient sky objects

The difference between a variable object and a transient object can be defined in part by the unpredictable nature of the phenomenon and from the observational point of view on the detection limit of the instrument, a variable object remaining detectable at any time while a transient source falls below the detection limit. In both cases, the time scales of variation can be different. Another aspect that highlights the difference between the two categories is the impact of variability on the very nature of the object. A source can be variable not by an intrinsic change in its composition but by an external effect such as the transit of a planet in front of a star that modifies the brightness of the target star for the observer. In the case of a transient source, the change of state is followed by a profound physical transformation of the system causing in some cases (gamma bursts or supernova) the death of the host star. The study of the transient sky thus makes it possible to better understand phenomena such as the processes of matter accretion in binary systems, ejections in the form of jets in gamma-ray bursts, the behaviour of a plasma in the presence of intense magnetic and gravitational fields or the coalescence of two compact stars. Transient objects can belong to the Milky Way or be located at much greater distances such as active galaxy nuclei. They are observed today in different wavelengths.


The video above illustrates the highly variable nature of the sky when observed at certain wavelengths. The sequence results from the continuous observation of the sky (represented here in galactic coordinates) by the ASM instrument of the RXTE space mission in the X-ray domain (between 5 and 12 keV) during the period 1996-1999, i.e. 4 years of data. Sources appear suddenly or suddenly change in brightness. They are mainly distributed along the galactic plane (figure at the bottom) and for the most remarkable their name is shown. Credit: http://xte.mit.edu/.

The transient sky and the SVOM mission: strategy and observation program

While the main goal of the SVOM mission is to ensure the observation of about 100 gamma-ray bursts per year, it is also a formidable tool for probing the transient sky. To observe phenomena occurring on short time scales (sometimes less than a second), significant detection and monitoring devices are required. Like its sister mission SWIFT, developed by NASA, the SVOM mission leaves an important place in its observation program for the non-GRB science. SVOM will be able to generate an alert after the detection of a transient phenomenon, thanks in particular to its large field of view instruments Eclairs and GRM. Conversely, the mission will be able to react to alerts (targets of opportunity, ToO) from other transient sky observatories, on the ground or in space, and then point its instruments towards the object. SVOM will thus be a partner of choice for other observation programs, in particular those dedicated to the study of the transient sky, such as the LSST project in the visible domain or by the SKA network in radio frequencies.

Multi-messenger astronomy

The mission will also be able to respond quickly to alerts from the IceCube or KM3N neutrino telescopes or from the LIGO and Virgo gravitational wave interferometers.
The initial goal of the mission, the study of gamma-ray bursts, will thus be extended to the study of gravitational waves. Predicted since Einstein and the theory of general relativity, these oscillations of the curvature of space-time became reality after the announcement on February 11, 2016 of their discovery by the LIGO/Virgo collaboration, crowning years of research and technological development. The signal detected on September 14, 2015 by the two interferometers of the LIGO project is interpreted as the signature of the very last moments of the fusion of two black holes of thirty solar masses each. This same network of interferometers detected another event on August 17, 2017, this time accompanied by a short gamma emission received by ESA’s Integral and NASA’s Fermi high-energy satellites. Here, the phenomenon observed both in the form of gravitational and electromagnetic waves corresponds to the fusion of two neutron stars, a hypothesis long advanced to explain short gamma-ray bursts.
These major discoveries confirm the coalescence scenario of two compact objects (neutron star and/or black hole) as a source of gravitational wave emission and open up new horizons for example their use as a potential cosmological probe.

Neutrino astronomy is another multi-messenger field where the SVOM mission can make a significant contribution by seeking in this case the electromagnetic counterpart of the neutrino signal, the first step towards source identification.

The challenges of the time domain

The study of the transient sky is a rapidly developing branch of astronomy and many observatories currently under development and dedicated to this topic will be set up by 2020. In this context, the scientific community faces many challenges. The main challenge is to process data in real time in order to detect transient phenomena as quickly as possible and to broadcast alerts effectively. The large amount of data and the number of people involved also require a specific organisation to ensure the effective diffusion and follow-up of alerts, a task and challenge that the project’s scientists are actively preparing.
A quarter of SVOM’s observation time will be dedicated to the detection of gamma-ray bursts, while 15% in the first two years and 40% in the third year will be devoted to transient phenomena (excluding bursts).

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Author : CEA / Irfu & Jesse Palmerio
The SVOM mission

The SVOM mission

The SVOM mission

The SVOM mission (Space-based multi-band astronomical Variable Objects Monitor) is a Franco-Chinese mission dedicated to the study of the most distant explosions of stars, the gamma-ray bursts. It is to be launched at the end of 2021 by the Chinese Long March 2C rocket from the Xichang launch base.
It is the result of a collaboration between the two national space agencies, CNSA (China National Space Administration) and CNES (Centre national d’études spatiales), with the main contributions of the Institute of Research into the Fundamental Laws of the Universe (Irfu) and the Research Institute of Astrophysics and Planetology (IRAP) for France and the National Astronomical Observatory (NAO) and the Beijing High Energy Institute (IHEP) for China.

The SVOM instruments (Space and Ground)

The SVOM instruments (Space and Ground)

The mission consists of 4 main instruments of which 2 are French (ECLAIRs and MXT) and 2 are Chinese (GRM and VT):
The ECLAIRs telescope to detect and localise gamma bursts in the X-ray band and low-energy gamma rays (from 4 to 250 keV).
The MXT telescope (Microchannel X-ray Telescope) for the observation of gamma burst in the soft X-ray range (0.2 to 10keV).
The GRM (Gamma Ray Burst Monitor) to measure the spectrum of high-energy bursts (from 15 keV to 5000 keV).
The VT telescope (Visible Telescope) operating in the visible range to detect and observe the visible emission produced immediately after a gamma burst.
The satellite weighs a total of 930 kg for a payload of 450 kg. It will be placed in a low earth orbit with an inclination of 30 degrees, an altitude of 625 km and an orbital period of 96 min.

Observations from space will be complemented by a large ground segment consisting of :
The wide-field camera GWAC (Ground-based Wide Angle Camera) to study from the ground in the visible range, the prompt emission of part of the bursts detected.
The robotic telescopes GFTs (Ground Follow-up Telescopes) to accurately measure the coordinates of the gamma-ray burst.

svom_2

The SVOM instruments (Satellite Qualification Model, December 2019). SECM/CNES/CEA

 

SVOM_QM_Integration

The qualification model of the SVOM satellite in integration in Shanghai, December 2019. Credit: SECM

 

Le modèle de qualification du satellite SVOM à Shanghai pendant les essais en vide thermique, octobre 2019, crédit SECM.

The qualification model of the SVOM satellite in Shanghai during thermal vacuum testing, October 2019. Credit: SECM.

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Author : CEA-Irfu

Gamma-ray burst, catching messages from the past

Although the early ages of the Universe are shrouded in mystery, enormous flashes of light upset the apparent calm. They come from violent explosions that emit vast amounts of high-energy radiation. These « Gamma-Ray Bursts » are the most energetic events observed since the Big Bang. They are fleeting and unpredictable, yet their origin is uncertain. What physics are they hiding? Are they the messengers of the first stars of the Universe? Do they allow us to probe the past? These are the questions that SVOM aims to study.

A race against time

SVOM, the Space-based multi-band astronomical Variable Objects Monitor, needs to have a wide range of capabilities. Its first task is to locate the flash of gamma rays. They can appear anywhere in the sky, and they only last a few seconds. Gamma rays do not penetrate the earth’s atmosphere, so detection must take place in space. Using a worldwide network of antennae, the results from the instruments on the SVOM satellite will be transmitted to Earth to enable other facilities to study the burst. The major challenge of the mission is to determine the origin of gamma-ray bursts: what environment do they come from? At what period are they created? Only the detailed spectral analysis of their light can answer these questions; this is a task for the large terrestrial telescopes that will study their emission following the GRB.

L'analyse conjointe de la lumière récoltée par les instruments au sol et dans l'espace, permettra de déterminer l'origine du sursaut.

The joint analysis of the light detected by ground and spaced instruments will provide a precise location of the source of the burst.

SVOM will provide a precise location of the burst, and measure the initial explosion energy and intensity. Coordinated observations over a wide range of wavelengths from space and from the ground are the key to fullest understanding this astronomical phenomenon.

Witnesses of the past

Examined in all possible ways, gamma-ray bursts will no longer be seen as mysterious objects, but rather as great tools for understanding the unknown. They will provide information on the conditions of their formation, allowing us to better understand extreme astrophysics. Witness of the past; they will give indications of their host galaxies, and also on the Universe illuminated by their distant light.

Opportunity to study the transient sky

Thanks to the remarkable combination of instruments deployed both on the ground and on-board the satellite, SVOM enables a wide range other scientific studies. Research teams around the world can take advantage of this automated technology to observe transient cosmic phenomena, such as ephemeral objects or whose brightness varies over time; examples could include supernovae and sources of gravitational waves. The powerful capabilities of SVOM will ensure that it is an essential partner for the entire scientific community.

A Franco-Chinese mission

The SVOM project is the result of collaboration between France and China. Scientific teams from both countries have pooled their expertise for the design and implementation of the different instruments. The satellite is scheduled for launch in 2021 under the supervision of the two national space agencies, CNSA (China National Space Administration) and CNES (Centre National d’Etudes Spatiales).

Une mission Franco-Chinoise

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Author : CEA / Irfu & Julian Osborne

History of a solved mystery

The discovery of gamma-ray bursts is recent. The first detection of this phenomenon was carried out by one of the military satellites of the Vela project, which began in 1963. During the Cold War, the United States and the USSR kept an eye out for the slightest act of belligerence, and particularly for nuclear tests. Despite the treaty on the prohibition of atomic tests in the atmosphere and space (signed in August 1963), the American army launched a reconnaissance mission to identify such traces. The Vela satellites were equipped with detectors of gamma-rays, X-rays and neutrons. On July 2nd 1967, the detectors went off: a very brief emission had been detected. After verification, it was clear that this gamma radiation was not of human origin, nor even terrestrial. But it was not until 1973 that this discovery was made public, once the military confidentiality had been lifted. Gamma-ray bursts quickly aroused the curiosity of the scientific community. There were many questions. What is the source of such flashes of light? By what mechanism(s)? Do they appear in our galaxy, the Milky Way, or in more distant galaxies, which would imply an even more colossal energy?

The map of the bursts

From 1991 onwards, NASA was able to collect crucial information thanks to the COMPTON space observatory, a giant satellite on which the Burst And Transient Source Experiment (BATSE) instrument was located. This mission revealed that gamma-ray bursts are divided into two distinct groups:

– short bursts (about 30% of the detected bursts) with high characteristic energy (about 1000 keV). Their duration is less than 2 seconds

– long bursts (70%) with a lower characteristic energy (of the order of 100 keV) and whose duration can reach several tens of minutes.

The BATSE experiment allowed the detection of more than 2500 gamma-ray bursts between 1991 and 2000 and a map of the sky was established. But for lack of a precise localization (a few square degrees) it was not possible to cross-identify bursts with celestial sources.

img_mission04

Each point on this sky map represented in galactic coordinates is a gamma-ray burst detected by BATSE. The color corresponds to the total energy perceived. BATSE detected 2704 gamma bursts between 1991 and 2000. In the coordinate system of this map, the center of the Milky Way is located in the center. Credits: NASA

This distribution is « isotropic »: the bursts are distributed randomly on the map indicating that they are either very close to the Earth, or very far, of extragalactic origin. No concentration of bursts along the plane of the Milky Way, symbolized on the map by the horizontal center line, appears. This most likely excludes candidates from our galaxy.

Broadening the field of study and deciphering distant sources

To determine the origin of gamma-ray bursts, it became necessary to locate them precisely in order to measure their distance. In April 1996 the Italian satellite BeppoSAX was launched. On 27 February 1997, the instruments on board the BeppoSAX satellite detected and localized the burst GRB970228. The precise location of the burst in the X-rays, rapidly transmitted to the ground, allowed scientists to point powerful ground telescopes located in La Palma in Spain towards the source. A weak and decreasing signal was detected. Thus, the existence of an afterglow emission was discovered. This late-time, weaker emission radiates in the X-rays, optical and radio waves. This discovery was pivotal: while X-rays and gamma rays are only observable from space, these other types of radiation allow partial follow-up from Earth! This eventually opened up a new field of study focused on the follow-up of gamma-ray bursts.

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Emission rémanente du sursaut GRB970228 captée dans les rayons X : le phénomène va en s’atténuant avec le temps. crédits : NASA ASI/BeppoSAX

Afterglow emission of the burst GRB970228 captured in the X-rays: the brightness decreases with time. Credits: NASA ASI / BeppoSAX

A few months later on May 8th 1997, GRB970508, a new burst, was detected and localized in the X-rays by BeppoSAX. The precise localization of the burst allowed the Keck telescope on Hawaii to be pointed in its direction and thanks to the afterglow emission, a spectral analysis was performed. This allowed for an estimation of the burst’s distance with its redshift measurement (see also « Measurement Tools »). The redshift is a change in the wavelength of radiation in space, when its source moves away from the observer (Doppler effect): the higher the redshift, the farther away the source is. For the first time, the distance of a burst was calculated. In the case of the long burst GRB970508, the calculated redshift is 0.835, which is equivalent to 6 billion light years! The hypothesis of an extragalactic origin of the bursts was thus verified. It became clear to the community that a better understanding of gamma-ray bursts would involve the rapid transmission of a precise localization of the burst to a reactive network of ground-based telescopes.

Collaborating between ground and space

In October 2000 saw the launch of the HETE-2 (High Transient Explorer) mission take place. One of its specificities was to have a processor on board to rapidly calculate the position of the burst. Once the coordinates were established, they were sent to Earth via a radio transmitter and received by a network of 15 relay antennas deployed on the surface of the globe under the satellite’s path. This strategy made it possible to discover the afterglow of a short burst (GRB050709). The European satellite, INTEGRAL (INTErnational Gamma Ray Astrophysics Laboratory) was launched in orbit in 2002 and applied the coded mask technique for the detection of gamma-ray bursts. This mission, still in operation, discovered the polarization of the prompt emission of the bursts, reinforcing the fireball model.

Le masque codé de l’imageur IBIS

The coded mask of the imager IBIS (Imager on Board the INTEGRAL Satellite). Credits: Integral Science Data Center, University of Geneva

 

L’un des deux télescopes robotiques TAROT (Télescope à Action Rapide pour les Objets Transitoires), précurseur dans l’observation optique automatisée. Celui-ci est installé sur le plateau de Calern dans le sud de la France, l’autre se trouve à La Silla au Chili.

One of the two robotic telescopes TAROT (Rapid Action Telescope for Transitory Objects), a precursor in automated optical observations. This one is installed on the plateau of Calern in the south of France, the other one is in La Silla in Chile.

The SWIFT era

In 2004, a significant step was taken with the launch of the NASA SWIFT satellite equipped with a large field gamma telescope and a very sensitive X-ray camera. Another specificity of this mission is its particularly agile platform, which allows it to quickly slew in the direction of the burst in order to study its afterglow emission. By way of example, SWIFT detected on 23 April 2009 the most distant gamma ray burst to date: GRB090423. Its distance is estimated at 13 billion light years (redshift of 8.2) making it one of the most distant objects ever observed. This burst comes from the death of a massive star that took place 630 million years after the Big Bang (as a reminder, the Big Bang took place 13.7 billion years ago). This event testifies to the early ages of the Universe.

Le système d’alerte de la mission SWIFT repose sur l’ombre portée à travers un masque codé. Les motifs du masque sont réalisés grâce à un algorithme. Crédits : NASA

The alert system for the SWIFT mission is based on the shadow created by coded mask. The patterns of the mask are created with an algorithm. Credits: NASA

Ground robotic telescope networks were set up to monitor and study the alerts broadcast by the SWIFT satellite. For example, the TAROT telescope was specifically designed to target transient objects as quickly as possible. On September 4th 2005, this telescope allowed us to study the light emitted by the gamma-ray burst GRB050904, which took place when our Universe was only 900 million years old, or 7% of its present age. With a mirror of only 25 cm in diameter, TAROT detected an object located 12.8 billion light years away, which highlights the high energy aspect of gamma-ray bursts. The latest mission, the NASA Fermi satellite sent to orbit in 2008, extends the study of the prompt emission to higher energy bursts. Fermi notably detected GRB080916C, a gamma-ray burst whose released energy makes it the most violent electromagnetic explosion ever observed.

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Author : CEA / Irfu & Jesse Palmerio

Probes of the distant Universe

Thanks to the possibility of observing the gamma-ray bursts in the optical and infrared, it is now known that they occur in very distant galaxies, so remote that some of them are listed as the most distant objects measured today. Considering the finite velocity of light, looking at far away objects is equivalent to looking back in time, to the past! Like ephemeral lighthouses in the cosmos, gamma-ray bursts allow us to probe the Universe at different times in its history and to better understand how galaxies formed over time.

Always further

These flashes are promising tools to probe the early Universe and therefore to be able to study its content and the different stages in its evolution. For example, the most distant burst identified to date, GRB090423, occurred 630 million years after the Big Bang, when the Universe was still in its prime youth.

img_mission09

Infrared image of gamma-ray burst counterpart GRB090423 obtained with the GEMINI telescope located in Hawaii. Credits: Gemini Observatory / NSF / AURA, D. Fox & A. Cucchiara (Penn State U.), and E. Berger (Harvard Univ.)

This long burst comes from a « collapsar »: the explosion of a very massive star that collapsed on itself under the effect of its own gravity. With a mass of at least 20 to 30 times the mass of the Sun, this rare star could be among the very first generations of stars. These stars, called « population III » stars, would be very massive, luminous and made up of only a few light elements (hydrogen, helium). They would have been formed barely 400 million years after the Big Bang but it is still unclear how. Their lifespan is short: a few million years. They are supposed to be partly responsible for the formation of other elements (heavier than hydrogen and helium) detected today in the local Universe. Gamma-ray bursts can thus inform scientists about the environment in which these stars are born. They thus contribute to the understanding of stellar evolution in the primordial Universe.

img_mission10

An artist’s view showing the incredible luminosity of the first generations of stars in the CR7 galaxy, located at 12.9 billion light years. These stellar populations could be partly composed of very massive stars, some of which would be at the origin of distant gamma ray bursts. Credits: ESO / M. Kornmesser

Furthermore, another interesting aspect of gamma-ray bursts consists in using their signal as a background light that successively crosses different regions between the burst and the Earth. These successive environments are crossed at different distances between the burst and us and therefore at different times. The imprints left in the light of the burst could then give indications on the elemental composition of the Universe throughout its history.

Gamma-ray bursts: a laboratory of extreme physics

The overwhelming energy of the burst, the velocity of the ejected particles and the successive shocks with the surrounding environment are all elements that classify gamma-ray bursts as laboratories of extreme physical conditions which in many cases are impossible to reproduce here on Earth.

The accelerated particle energy is orders of magnitude (up to one million) beyond what the most powerful terrestrial machines like the Large Hadron Collider (LHC) can produce today. Therefore, the study of physical processes in these extreme conditions makes it possible to better understand the conditions in other classes of objects.

One example of this is the nature and energy of particles propelled in jets at relativistic velocities, which is a phenomenon also evoked to explain the origin of eruptive episodes observed in blazars (active galaxies harboring a supermassive black hole of several million solar masses).

Gamma-ray bursts are also promising sources of neutrinos and very high energy cosmic radiation.

Extremely massive stars (hundreds of solar masses), according to several scenarios, cause a particular class of bursts: extremely distant, long bursts. The study of bursts as a consequence of the explosion of stars is a tool of choice to better identify the first generation of stars (called “population III” stars) and star formation in the early epochs of the universe. Another singular aspect of gamma-ray bursts regarding short bursts is the possibility that they are sources of gravitational waves. The coalescence of two compact objects (neutron star and / or black hole) is a likely scenario to explain this short bursts. Nevertheless, the different fusion phases or the product of the coalescence are still poorly understood. A common gamma-ray burst – gravitational wave detection would allow significant advances.

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Author : CEA / Irfu & Jesse Palmerio

Measurement Tools

In 1997, an afterglow associated with a gamma ray burst was discovered by the Italian satellite BeppoSAX. The afterglow corresponds to the extension of the emission into the X-ray, visible and radio domains, immediately after the flash in gamma-rays (the prompt emission). This discovery was essential because it enabled scientists to determine for the first time the distance of a burst and the physical properties of its surrounding environment. This opened up a new field of research to the scientific community. While the prompt emission lasts only a few seconds, the afterglow persists for a longer period of time, hours or days depending on the wavelength range. This has an immediate consequence; the afterglow can be studied in detail in the visible and infrared by telescopes on the ground provided they have a refined position of the source in the sky. Spectroscopic studies are a key point at this stage because they provide a wealth of diverse information on the distance, the properties of the burst’s environment, the type of host galaxy, and the nature of the media probed by the light during its journey to Earth. Therefore spectroscopy is an extremely powerful and indispensable measurement tool in order to use bursts as probes of the distant universe.

Spectral lines

A spectrometer placed at the end of a telescope makes it possible to decompose the light of the observed source in order to establish its spectrum. The spectrum of a source acts as a fingerprint revealing its true identity.

Raies spectrales

On the left, the spectrum of a solid, a liquid or a very dense gas is continuous. In the middle, the spectrum of a cold gas placed in front of  a continuous source reveals dark streaks called absorption lines. On the right, the spectrum of a hot gas is composed of bright lines called emission lines

It is characterized by the presence of spectral lines, situated at specific wavelengths depending on the chemical elements of the source. By analyzing the spectrum of a medium, it is therefore possible to determine the chemical composition of the observed object. These spectral lines can be of two natures. When they come from an ionized gas, like the gas of the interstellar medium heated by the radiation of stars, they are observed in emission. For example, the lines of ionized hydrogen and oxygen are commonly observed in the spectra of galaxies where significant stellar formation is taking place. Conversely, if the light of the observed source passes through clouds of neutral gas, the chemical elements in the cloud can absorb some of the photons, and lines appear in the spectrum: the lines are then observed in absorption. In the case of gamma-ray bursts, the spectral analysis of the afterglow emission reveals in a quasi-systematic way a multitude of absorption lines coming from all the absorbing media crossed by the light of the burst. These absorbers include the gas of the circumburst environment and the interstellar medium of the host galaxy, as well as absorbers beyond the host galaxy, located between the burst and Earth. The spectral analysis of afterglows thus provides crucial information not only on the chemical composition of the environment in which the gamma-ray bursts occur, but also on the properties of galaxies and their evolution at different epochs of cosmic history.

The Doppler effect or using redshift to measure distance

The wavelength of a spectral line can also translate a motion of the emitting source : the Doppler effect. When an emitting source is moving towards the observer, its apparent wavelength becomes shorter, it is shifted on the spectrum. In the visible domain, this means that it shifts towards bluer wavelengths. Conversely, when the source moves away, its apparent wavelength increases. This is called redshift, and the faster the source moves, the greater the spectral shift. This property is particularly interesting in astronomy, since the expansion of the Universe leads to a redshift of the spectra of galaxies. The magnitude of this redshift is directly related to the distance of the observed source. This is the law discovered by Edwin Hubble in 1929. Thus, each absorbing system crossed by a gamma-ray burst produces spectral lines in the spectrum of the afterglow, and the wavelength shift of these lines allows us to measure the distance to the medium responsible for the absorption. In particular, the very first absorber encountered by the light of the burst is the gas present in its close environment and has the largest spectral offset.

Redshift

The further away from Earth, the greater the redshift of galaxies

The redshift ideally allows scientists to identify the galaxy in which the burst took place. It is measured by the absorption lines of the afterglow emission. The redshift obtained by the emission lines of the host galaxy detected after the disappearance of the afterglow is generally identical to the one measured in absorption. This method confirms that this is the host galaxy. Detection is only the starting point of astronomy. Beyond the simple observation of a luminous point, it is necessary to be able to describe what constitutes these distant environments and to perhaps deduce the conditions under which gamma-ray bursts form. Spectroscopy can thus, depending on the scale, allow us to know the atmosphere close to a star, a planet, what a galaxy, or even what the primordial matter that appeared just after the Big Bang is made of.

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Author : CEA / Irfu & Jesse Palmerio

What is a gamma-ray burst ?

Manifestation of a gigantic explosion, these flashes of light are considered to be the brightest and most energy-rich events since the Big Bang.

Un sursaut gamma s’accompagne d’un dégagement de matière sous forme de deux cônes opposés. https://www.eso.org/public/france/images/eso0917a/

A gamma-ray burst is accompanied by a release of material in the form of two opposite cones. Credit: ESO

These are rare events on the scale of a galaxy, yet it would be possible to observe on average ten per day.
The power that emerges is considerable, the equivalent of more than a billion billion suns. This makes them visible at very large distances, even beyond our galaxy. However, their detection is difficult and real technical prowess is needed to observe the random and unpredictable gamma-ray bursts.

A rush of gamma photons

These explosions are called « gamma-ray » in reference to the particles of very high energy initially released: gamma photons. Just like visible light, X-rays or radio waves, these are  electromagnetic waves.

Les rayons gamma (?) sont les ondes de plus petites longueurs d’onde (?) du spectre élecromagnétique. Le spectre de la lumière visible, à titre indicatif, est représenté par les couleurs selon la longueur d’onde croissante.

Gamma rays are the electromagnetic waves with the smallest wavelengths in the electromagnetic spectrum. The spectrum of visible light, as an indication, is represented by the colors.

The energy of a photon is measured in electron-volt (eV), a photon of visible light emits about 2eV. That of a gamma photon can reach several billions of electrons-volts!

Birth of a gamma ray burst

The explosion at the origin of the burst fulfills specific conditions. Today two scenarios explain the power and rapid variation of gamma ray bursts: the coalescence or fusion of two compact objects (neutron star or black hole) and the collapse of a very massive star.
The majority of gamma ray bursts recorded today indicate that they appear during the death of a very massive star. Indeed, under the scenario of the collapse of a star at the end its life, this one must be very massive to provide the energy required for the ejection of matter at very high speed. It is this material, when propagated in the surrounding environment, that will allow the transformation of this energy into gamma radiation.
At the moment of the explosion, we can distinguish several stages explaining the appearance of the burst, according to the so-called « fireball » model:

Illustration du modèle de la boule de feu. Crédits : NASA

Illustration of the fireball model. Credit : NASA

  1. The progenitor produces jets of material consisting essentially of packets of electrons, ejected in sporadically in a particular direction. These packets are expelled at different speeds but all close to the speed of light. These jets are therefore said to be ultra-relativistic.
  2. Very violent shocks take place when these packets of electrons come into contact with each other: it is the model of the internal shocks. The layers of material expelled at different speeds end up colliding, the fastest layers catching up with the slowest. These shock fronts will abruptly generate gamma rays. This is called the prompt emission.
  3. There are also external shocks where these same layers of matter interact later with the surrounding environment of the progenitor. This gives rise to less intense, less energetic radiation, which is spread out over time and composed of X-rays, visible light and radio waves. This is called the afterglow emission.

The conditions of appearance

The duration of the burst indicates two possible origins:
When the duration is less than 2 seconds, the burst is called a short burst. It would come from the coalescence of two massive and compact objects such as two neutron stars, or a neutron star and a black hole.
These two stars, in orbit, end up « falling » on each other as they lose energy by the emission of gravitational waves. From this ultimate encounter a new black hole is born.
In the case of long bursts, those lasting more than 2 seconds, they are produced at the end of a hypernova, a type of supernova. A hypernova is a star whose mass is greater than 20 times that of the sun and which undergoes gravitational collapse. A black hole is created abruptly causing shock waves that explode the rest of the star and pierce the stellar envelope: the outer layers are violently expelled. This is called the fireball model.
In both cases,  the newly-formed compact object (probably a black hole) grows swallowing  the matter in its immediate surroundings in a matter of seconds and forms a thick, rapidly rotating accretion disk arond itself. A part of the matter attracted by the gravitational force of the black hole is expelled in the form of two opposing jets along the axis of rotation of the disc following a physical mechanism still far from being understood.
This ejection at very high speed generates the shocks previously described and reveals the gamma-ray burst, as a result of internal shocks. In order to perceive its light, the observer must therefore be aligned with the axis of emission.

The afterglow emission

The afterglow emission of a gamma-ray burst is the phase which follows the prompt emission. According to the fireball model, it is due to shocks which during their expansion will sweep the environment surrounding the progenitor, generating radiation at all wavelengths. Its study thus makes it possible to know the nature of the environment of the progenitor. The remanent emission is not as brief as the prompt emission. It gradually decreases on a timescale of hours, days or months. This makes it possible to carry out observing programs with ground or space telescopes, provided that there is a sufficiently precise position of the burst, in particular in the X-rays and in visible light. The information provided by the afterglow emission is crucial for a better understanding of the explosive phenomenon and the environment of gamma-ray burst progenitors.

The fading image of the optical afterglow of GRB 030329, as seen on April 3 (four days after the GRB event) and May 1, 2003. The images were obtained with the FORS 1 and 2 multi-mode instruments at the 8.2-m VLT telescopes.

On the left, image obtained on April 3, 2003 of the afterglow emission in optical of the burst appeared on March 29, 2003. Right, a month later, the emission is always visible but weaker because it decreases gradually. Credit: ESO

Nomenclature

GRB for Gamma Ray Burst, followed by detection date, yymmdd.
Example: GRB 970508 corresponds to a burst detected on the 8th of May 1997.

Video of the Youtube Channel « The Sense Of Wonder »

To discover, in a different way, the subject which we are passionate about.

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Author : CEA / Irfu & Jesse Palmerio

The transient sky

Variable and transient bodies have played a major role in astronomy for a long time, as shown by the observations of Chinese astronomers reported 4000 years ago (see the article). Comets, novae, variable stars, supernovae, gamma bursts or coalescence of compact objects causing the emission of gravitational waves are among the objects of this variable and transient sky, far from the classical representation of an unchangeable, static sky.
The rise and the interest in observing the transient sky are closely linked to the technological developments and progress of detection tools: more sensitive sensors, therefore shorter exposure times, access to new wavelength domains, increased power of storage and data processing resources, the advent of wide-field cameras mounted on increasingly large telescopes, their effectiveness and interaction with alerts given by the instruments developed in the field of non-magnetic messengers.

Variable and transient sky objects

The difference between a variable object and a transient object can be defined in part by the unpredictable nature of the phenomenon and from the observational point of view on the detection limit of the instrument, a variable object remaining detectable at any time while a transient source falls below the detection limit. In both cases, the time scales of variation can be different. Another aspect that highlights the difference between the two categories is the impact of variability on the very nature of the object. A source can be variable not by an intrinsic change in its composition but by an external effect such as the transit of a planet in front of a star that modifies the brightness of the target star for the observer. In the case of a transient source, the change of state is followed by a profound physical transformation of the system causing in some cases (gamma bursts or supernova) the death of the host star. The study of the transient sky thus makes it possible to better understand phenomena such as the processes of matter accretion in binary systems, ejections in the form of jets in gamma-ray bursts, the behaviour of a plasma in the presence of intense magnetic and gravitational fields or the coalescence of two compact stars. Transient objects can belong to the Milky Way or be located at much greater distances such as active galaxy nuclei. They are observed today in different wavelengths.


The video above illustrates the highly variable nature of the sky when observed at certain wavelengths. The sequence results from the continuous observation of the sky (represented here in galactic coordinates) by the ASM instrument of the RXTE space mission in the X-ray domain (between 5 and 12 keV) during the period 1996-1999, i.e. 4 years of data. Sources appear suddenly or suddenly change in brightness. They are mainly distributed along the galactic plane (figure at the bottom) and for the most remarkable their name is shown. Credit: http://xte.mit.edu/.

The transient sky and the SVOM mission: strategy and observation program

While the main goal of the SVOM mission is to ensure the observation of about 100 gamma-ray bursts per year, it is also a formidable tool for probing the transient sky. To observe phenomena occurring on short time scales (sometimes less than a second), significant detection and monitoring devices are required. Like its sister mission SWIFT, developed by NASA, the SVOM mission leaves an important place in its observation program for the non-GRB science. SVOM will be able to generate an alert after the detection of a transient phenomenon, thanks in particular to its large field of view instruments Eclairs and GRM. Conversely, the mission will be able to react to alerts (targets of opportunity, ToO) from other transient sky observatories, on the ground or in space, and then point its instruments towards the object. SVOM will thus be a partner of choice for other observation programs, in particular those dedicated to the study of the transient sky, such as the LSST project in the visible domain or by the SKA network in radio frequencies.

Multi-messenger astronomy

The mission will also be able to respond quickly to alerts from the IceCube or KM3N neutrino telescopes or from the LIGO and Virgo gravitational wave interferometers.
The initial goal of the mission, the study of gamma-ray bursts, will thus be extended to the study of gravitational waves. Predicted since Einstein and the theory of general relativity, these oscillations of the curvature of space-time became reality after the announcement on February 11, 2016 of their discovery by the LIGO/Virgo collaboration, crowning years of research and technological development. The signal detected on September 14, 2015 by the two interferometers of the LIGO project is interpreted as the signature of the very last moments of the fusion of two black holes of thirty solar masses each. This same network of interferometers detected another event on August 17, 2017, this time accompanied by a short gamma emission received by ESA’s Integral and NASA’s Fermi high-energy satellites. Here, the phenomenon observed both in the form of gravitational and electromagnetic waves corresponds to the fusion of two neutron stars, a hypothesis long advanced to explain short gamma-ray bursts.
These major discoveries confirm the coalescence scenario of two compact objects (neutron star and/or black hole) as a source of gravitational wave emission and open up new horizons for example their use as a potential cosmological probe.

Neutrino astronomy is another multi-messenger field where the SVOM mission can make a significant contribution by seeking in this case the electromagnetic counterpart of the neutrino signal, the first step towards source identification.

The challenges of the time domain

The study of the transient sky is a rapidly developing branch of astronomy and many observatories currently under development and dedicated to this topic will be set up by 2020. In this context, the scientific community faces many challenges. The main challenge is to process data in real time in order to detect transient phenomena as quickly as possible and to broadcast alerts effectively. The large amount of data and the number of people involved also require a specific organisation to ensure the effective diffusion and follow-up of alerts, a task and challenge that the project’s scientists are actively preparing.
A quarter of SVOM’s observation time will be dedicated to the detection of gamma-ray bursts, while 15% in the first two years and 40% in the third year will be devoted to transient phenomena (excluding bursts).

Infos

Author : CEA / Irfu & Jesse Palmerio

A Franco-Chinese collaboration

The SVOM mission was decided following an intergovernmental agreement between France and China, specified in a memorandum of understanding in 2014.
It is a cooperation between the Chinese Space Agency (CNSA), the Chinese Academy of Sciences (CAS), and the French Space Agency (CNES) which manages the development of the French payload (ECLAIRs and MXT instruments), the antenna network (alert system) and the French scientific center.

The SVOM collaboration during the PDR review in Yantai (July 2016).

The SVOM collaboration during the PDR review in Yantai (July 2016).

The launch of the preliminary study phase (Phase B) of the SVOM mission was formalized in 2014. This phase concluded with a preliminary design review (PDR) in July 2016.
The detailed studies phase (Phase C) was launched in January 2017.
The launch of the SVOM mission is scheduled for the end of 2021.

Infos

Author : CEA / Irfu

The consortium

Les intervenants français et collaborateurs sont :

 

Centre National d’Etudes Spatiales CNES
Maître d’œuvre du projet SVOM
Maitre d’œuvre du télescope ECLAIRs
Maitre d’œuvre du télescope MXT

Institut de Recherche sur les lois Fondamentales de l’Univers CEA/IRFU
Responsabilité scientifique de la mission SVOM
Responsabilité scientifique de l’instrument MXT
Responsabilité scientifique du segment sol français
Maître d’œuvre du développement du centre d’expertise scientifique FSC (French Science Center)
Maître d’œuvre du développement du centre d’expertise de l’instrument MXT
Participation au développement de l’instrument ECLAIRs (logiciel trigger)
Participation au développement de l’instrument MXT (caméra-X)
Participation au développement du télescope robotique F-GFT (design optique)

Institut de Recherche en Astrophysique et Planétologie CNRS/IRAP
Responsabilité scientifique de l’instrument ECLAIRs
Participation au développement de l’instrument ECLAIRs (caméra gamma DPIX)
Maître d’œuvre du développement du centre d’expertise de l’instrument ECLAIRs
Participation au traitement des données scientifiques de l’instrument ECLAIRs
Maître d’œuvre du développement du télescope robotique F-GFT (French – Ground Follow-up Telescope)
Maître d’œuvre du développement de la caméra infrarouge CAGIRE du F-GFT

Laboratoire d’Astrophysique de Marseille CNRS/LAM
Co-responsabilité scientifique de la mission SVOM
Responsabilité scientifique du télescope robotique F-GFT
Responsabilité scientifique de l’organisation du suivi sol (Follow-up)
Participation au développement du télescope robotique F-GFT
Participation au traitement des données scientifiques de la mission

AstroParticules et Cosmologie APC
Responsabilité scientifique de la science hors sursauts
Responsabilité scientifique des activités multi-messagers
Participation au développement de l’instrument ECLAIRs (masque codé)
Participation au traitement des données scientifiques de l’instrument ECLAIRs

Institut d’Astrophysique de Paris IAP
Responsabilité scientifique du programme dédié aux sursauts
Participation au traitement des données scientifiques de la mission

Observatoire Astronomique de Strasbourg CNRS/OAS
Participation au traitement des données de l’instrument MXT

Laboratoire Univers et Particules de Montpellier CNRS/LUPM
Participation au traitement des données scientifiques des instruments ECLAIRs et GRM

Centre de Physique des Particules de Marseille CNRS/CPPM
Maître d’œuvre du développement du centre d’expertise du télescope robotique F-GFT

Observatoire de Paris CNRS/GEPI
Participation au traitement des données scientifiques de l’instrument VT (Visible Telescope)

Laboratoire de l’Accélérateur Linéaire CNRS/LAL
Développement de l’interface entre SVOM et les observatoires multi-messagers
Participation au développement de l’instrument MXT (logiciel scientifique)

Observatoire de Haute Provence CNRS/OHP
Participation au développement du télescope robotique F-GFT

Université de Leicester
Définition du système optique « Lobster eye » du télescope MXT
Assemblage et intégration du système optique du télescope MXT

Max-Planck Institut für Extraterrestrische Physik MPE
Fourniture du détecteur X de la caméra MXT
Etalonnage des instruments ECLAIRs et MXT auprès de la source X Panther

Université Nationale Autonome du Mexique UNAM
Hébergement du télescope F-GFT sur le site de San Pedro Martyr
Fourniture de la caméra visible du F-GFT
Opérations et maintenance du F-GFT

Les intervenants chinois sont :

Shanghai Engineering Centre for Microsatellites SECM
Maitre d’œuvre du satellite SVOM

National Astronomical Observatory of China NAOC
Responsabilité scientifique de la mission SVOM
Responsabilité scientifique de l’instrument VT
Responsabilité scientifique du télescope robotique C-GFT (Chinese – Ground Follow-up Telescope)
Responsabilité scientifique de l’instrument sol GWAC (Ground Wide Angle Camera)
Responsabilité scientifique du segment sol chinois
Maître d’œuvre du développement du centre d’expertise scientifique chinois CSC (Chinese Science Center)

Institute of High Energy Physics IHEP
Co-responsabilité scientifique de la mission SVOM
Responsabilité scientifique de l’instrument GRM (Gamma Ray Monitor)
Maitre d’œuvre de l’instrument GRM

National Space Science Center NSSC
Maitre d’œuvre du centre de contrôle de la mission SVOM

Xi’an Institute of Optics and Precision Mechanics XIOPM
Maitre d’œuvre du télescope VT (Visible Telescope)

Infos

Author : CEA / Irfu
ECLAIRs: on the flip of a coin

ECLAIRs: on the flip of a coin

ECLAIRs: on the flip of a coin

ECLAIRs: Integration of the flight model detection plan completed, after the « front » side, it is the « back » side that has just been integrated.

After the « face » side and its 6400 detectors in the spring, it is now the « back » side of the detection plan that the IRAP teams have just integrated into the CNES clean rooms.  It consists of installing the 8 « interface board » cards that provide the interface between the detection plan and the reading electronics. In practice, it is above all necessary to check the correct operation of the 3800 connection points with the detection modules and the 72 harnesses allowing connection to the reading electronics. When we know that just one year ago, it was necessary to urgently restart the manufacture of a batch of flight model cards following the rejection of several of them due to a manufacturing problem, it is quite a challenge that IRAP, accompanied by the experts of the CNES, took up to deliver the detection plan within the deadline.

ECLAIRs_pile_face

Detection plane of the ECLAIRs instrument, « front » side on the left and « back » side on the right

IRAP is now preparing the integration of the electronic modules for power supply, configuration and reading of the detection plan. The coupling of the system and the first signals are expected in the first half of October.

ECLAIRs: Delivery of the flight model calculator

ECLAIRs: Delivery of the flight model calculator

ECLAIRs: Delivery of the flight model calculator

The flight model of the UGTS, Scientific Processing and Management Unit, has just arrived in the clean room.

The ECLAIRs instrument’s flight computer unit, the UGTS (Unité de Gestion et de Traitement Scientifique) has just been delivered by the company EREMS (Etudes et réalisations électroniques Développements logiciels). The UGTS will provide the electrical and command/control interfaces with the satellite on the one hand and with the DPIX camera developed by IRAP on the other. Equipped with flight software currently being developed at CEA, it will process the data provided by the camera onboard in order to detect gamma-ray bursts in real time.

Reception and control of the UGTS flight model in room Signe-3 at CNES

Reception and control of the UGTS flight model in room Signe-3 at CNES

After a phase of appropriation and testing by the CNES AIT (Assembly, Integration and Test) teams, the UGTS should be connected to the DPIX camera by the end of October.

Flight model of the UGTS

Flight model of the UGTS

Infos

Author : Philippe Guillemot (CNES)
MXT in the spotlight of Panter

MXT in the spotlight of Panter

MXT in the spotlight of Panter

The MXT Performance Model successfully tested at MPE Panter X-ray beam facility

A campaign dedicated to the verification and validation of the performance of the different modules (optics, camera, electronics) of SVOM’s MXT telescope has been successfully conducted at the Panter X-ray beam facility located near Munich. The results validate the concept of the MXT instrument and push the MXT project to new steps before its installation on the SVOM satellite platform in 2021.

In February 2020, the MXT teams (CNES, CEA, University of Leicester, MPE and IJCLAb-Orsay, gathered at Panter X-ray testing facility near Munich, in order to perform a full end-to-end test of the MXT Performance Model. The telescope, composed by the optics qualification model (QM), the camera performance model (PM) had been integrated at CNES Toulouse and shipped to Panter at the end of January. All the elements were flight representative in terms of performance (except for the focal length, that is slightly shorter than the flight model one) and allowed to validate for the first time a complete system composed of a “Lobster-Eye” telescope in a narrow field configuration.

The MXT Team is celebrating the end of the Performance Tests campaign in Panter!

The MXT Team is celebrating the end of the Performance Tests campaign in Panter!

After setting up and validating the thermal environment, the performance tests took place for two weeks, during which scientists and engineers were able to test different aspects of the telescope. 170 science runs have been acquired in order to answer to the planned scientific goals.

MXT PM subsystem ready to be integrated at CNES Toulouse: on the top the MXT optics, at the bottom right the camera, and at bottom left the structural tube.

MXT PM subsystem ready to be integrated at CNES Toulouse: on the top the MXT optics, at the bottom right the camera, and at bottom left the structural tube.

The properties of the MXT point spread function (PSF) have been measured at different positions and energies over the entire operational range (0.2-10 keV). At 1.5 keV the PSF FWHM was measured to be 9.6 arc min, with a negligible level of vignetting over the entire field of view.

Left: MXT PSF obtained with a C-K source (0.28 keV). Right: MXT PSF obtained with a Ge-K source (9.88 keV).

Left: MXT PSF obtained with a C-K source (0.28 keV). Right: MXT PSF obtained with a Ge-K source (9.88 keV).

The Panter tests allowed us also to measure the spectral performance of the telescope over its entire energy range: the MXT camera has confirmed to be a low-noise system with state-of-the-art spectral capabilities. As an example, an Al-K source spectrum is shown (Fig. below). The energy resolution for single events measured at the MXT nominal operating temperature (~-70°C) is 78 eV, smaller than the instrument requirement of 80 eV. We were also able to explore different thermal configurations, and measure their impact on the telescope performance.

Al-K (1.49 keV) single events spectrum obtained with MXT during Panter tests

Al-K (1.49 keV) single events spectrum obtained with MXT during Panter tests

The next steps for the MXT telescope are the completion of the flight model sub-systems, their integration and the final end-to-end tests that will take place in Panter in about one year from now, just before shipping the telescope to China for final integration of the SVOM platform.

Infos

Author : CEA-Irfu
News 2020 July – « confined » review of the end of phase C (CDR)

News 2020 July – « confined » review of the end of phase C (CDR)

News 2020 July – « confined » review of the end of phase C (CDR)

The end-of-Phase C Review (Critical Design Review) was held by videoconference from June 29 to July 10, 2020.
The SVOM project has been strongly impacted by the covid-19 pandemic. At the end of January, the Chinese teams were confined and testing activities in Shanghai on the satellite qualification model were suspended. The Chinese teams gradually resumed work in March, but it was then the turn of the French teams to be confined… Today, activities have resumed in all the laboratories but travel is still severely restricted and we do not expect any meetings before late autumn or even early next year.

It is in this particular context that the end-of-phase C review was held. Since it could not be held in person, it consisted of a series of video-conferences spread over two weeks, scheduled in the morning in France and in the afternoon in China. The first week was devoted to presentations by the SVOM team and the second week was dedicated to questions/answers between the review group and the SVOM teams.

Group photo of the end-of-Phase C review. The review was held by videoconference from June 30 to July 11, 2020.

Group photo of the end-of-Phase C review. The review was held by videoconference from June 30 to July 11, 2020.

The objective of this review was to verify that the system developed for the SVOM mission meets the scientific requirements of the mission. After two weeks of discussion, the review group did not identify any major problems. The impact of the pandemic on the project as a whole was assessed and a delay of 5 months on the initial planning was noted. The launch of SVOM is now scheduled for early June 2022.
At the end of the meeting, the review group congratulated the SVOM team for the success of Phase C and encouraged them to continue in Phase D in the same spirit of cooperation.

Recall below the different phases of a space project:

– Phase 0: mission analysis
– Phase A: Feasibility study, concluded by the Preliminary Requirement Review.
– Phase B: Preliminary Design, concluded by the Preliminary Design Review.
– Phase C: detailed design, concluded by the Critical Design Review.
– Phase D: implementation and qualification
– Phase E: Operation

Infos

Author : CEA-Irfu
During the lockdown, the integration of the ECLAIRs detection plan

During the lockdown, the integration of the ECLAIRs detection plan

During the lockdown, the integration of the ECLAIRs detection plan

The flight model of the ECLAIRs instrument is beginning to take shape. During the period of lockdown, there were few people in the CNES clean room and above all a lot of calm. This moment was used by the IRAP team to carry out the integration of the 6400 detectors of the detection plan of the ECLAIRs instrument. Thus, 200 « XRDPIX » modules of 32 pixels each were patiently and meticulously checked, installed and aligned on the cold plate of the instrument during two weeks. This step crowns more than 15 years of efforts around the development and characterization of these detection modules. During this long period, 14,000 elementary detectors were supplied and carefully sorted, leading to the realization of just over 300 XRDPIX modules and the selection of the 200 best ones, which today constitute the detection plan of the ECLAIRs instrument flight model.

Integration of the last of the 200 XRDPIX modules of the ECLAIRs instrument flight model detection plan.

Integration of the last of the 200 XRDPIX modules of the ECLAIRs instrument flight model detection plan.

The next step is now to integrate, on the other side of the detection plane, the interface cards to supply power and read the detectors. The first electrical tests will then take place, before a mechanical characterization test scheduled for July.

"Mirror, my beautiful mirror, tell me..."

« Mirror, my beautiful mirror, tell me… »

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Author : Philippe Guillemot (CNES)
As a practice run for the SVOM satellite and the French instruments

As a practice run for the SVOM satellite and the French instruments

As a practice run for the SVOM satellite and the French instruments

Since September, the Chinese SECM and French CNES teams have been working together on the integration and environmental testing of the « qualification model » satellite. This satellite model is used to verify that all its components fit together correctly and that the assembly will be able to withstand the mechanical, thermal and electrical environments encountered during launch and life in orbit. It is also a kind of practice run of the activity that will be carried out on the « real » flight model satellite, a rehearsal during which both the procedures and the joint operation of the teams are tested. It should be noted that, although it is not the « real » satellite model at this stage, nor the real instrument models, these are accurate models designed to validate the overall mechanical, thermal and electrical behaviour.

For the French teams it started out with the integration of the ECLAIRs and MXT telescopes on the satellite. This is the moment when we check that what works in theory on a computer also works in real life. Like a Tetris, everything has to fit together correctly and the holes have to fall in front of the holes. The dexterity of the integration teams is heavily tested as the space available is limited and the screws to be tightened are not easily accessible. Nerves are severely strained, and everyone gives a big sigh of relief when everything falls into place and snaps into place.

Then it’s time to power up the satellite, check that everything is working and that the various instruments and subsystems are communicating with each other. The electrical and command/control teams take over from the mechanics to play out test sequences representative of the life of the instruments and satellite throughout the mission. Several tests of this type have already been carried out, so this phase is of little concern, but it is still a great satisfaction to see that everything is going normally.

After one month of operation, the satellite is now ready for environmental testing:

The joint Franco-Chinese team during the test campaign on the satellite qualification model, January 2020.

The joint Franco-Chinese team during the test campaign on the satellite qualification model, January 2020.

  • First, electrical tests known as auto-compatibility. The aim is to check that electrical disturbances produced by one piece of equipment do not interfere with the operation of the others, in other words, to test that « electrical » cohabitation goes well. For the French instruments, which are not at all representative in terms of performance, the aim is above all to gain a better understanding of the environment and the sources of disturbance to be encountered in flight.
SVOM satellite auto-compatibility tests, qualification model (Shanghai)

SVOM satellite auto-compatibility tests, qualification model (Shanghai)

  • This is followed by thermal tests during which the satellite is installed in a vacuum chamber that simulates a vacuum in space and undergoes several temperature cycles between the « cold case » and the « hot case » satellite. These tests, carried out continuously over several days, involve 3 x 8 operation of the teams. The predictions made prior to the tests predict temperatures for our instruments to be at their coldest around -70°C and at their warmest up to +40°C. While the primary objective is to verify that the instruments operate at such temperatures, it is also an opportunity to validate the temperature predictions and the thermal models that go with them. Finally, at the end of 3 weeks under vacuum, everyone holds their breath when the tank is opened and sees that the satellite has not suffered any degradation. Fortunately, everything is fine, so the tests can continue.
Thermal vacuum testing of the SVOM satellite, qualification model (Shanghai)

Thermal vacuum testing of the SVOM satellite, qualification model (Shanghai)

  • The last test sequence is certainly the most impressive as it involves shaking the satellite in all directions to check that everything holds together. The sequence takes place in 3 stages. First, the satellite, just like the instruments before it [See previous news], is installed on a vibrating pot. It will be shaken, axis after axis, according to a sinusoidal movement whose frequency, between a few hertz and 2000 Hz, and amplitude will be progressively varied.
SVOM stellite mechanical vibration tests, qualification model(Shanghai)

SVOM stellite mechanical vibration tests, qualification model(Shanghai)

  • Then the satellite is placed in an acoustic chamber. This is to reproduce the noise, using a set of giant trumpets, to which the satellite will be exposed during launch. Our ears would not resist it, but the satellite passes the test with ease.
Acoustic test of the SVOM satellite, qualification model (Shanghai)

Acoustic test of the SVOM satellite, qualification model (Shanghai)

  • Finally, it is time to check that the satellite can withstand the shocks associated with the deployment of the solar panels, when the screws holding them folded back on the satellite are cut by explosives. And there’s really nothing more efficient than deploying a solar panel in real size, which allows to check that the deployment is working properly.

 

After 5 months of activity in China, the satellite and its instruments passed all the tests to which they were subjected with success. It’s time to take a break, and for the French teams who have been taking turns since the beginning of September to take a rest. The next appointment is set for early February with the Chinese teams for final electrical tests. Unfortunately, current events in China have decided otherwise, forcing us to delay this final sequence. But that’s only a postponement.

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Author : Philippe Guillemot (CNES)
Environmental tests for MXT and ECLAIRs

Environmental tests for MXT and ECLAIRs

Environmental tests for MXT and ECLAIRs

Final step before the delivery of the STM telescopes of the French SVOM payload

This is the last step for our models before delivery in China, the CNES teams have just carried out environmental tests on 2 models of the ECLAIRs and MXT telescopes. The objective of these tests is to « qualify » (demonstrate) with sufficient margin the telescopes’ ability to withstand launch conditions and then the hostile space environment throughout the mission.

The purpose of these tests is not to test flight equipment but to test simplified models that are mechanically and thermally representative of future instruments. We are talking about STM models for Structural and Thermal Model. These STM models are defined in such a way as to accurately reproduce the mechanical (same interfaces, same mass, same manufacturing processes, same materials) and thermal (same power dissipation, same thermal leaks) behaviour of flight instruments. However, they are not equipped with detectors or electronic subsystems.

The tests of each telescope were carried out in 3 stages:

  • Mechanical vibration tests: the telescope is installed on a shaker, a kind of large loudspeaker that will shake the instrument energetically in various directions and at different oscillation frequencies. Two types of solicitations are applied, sinusoidal and random solicitations. Sinusoidal tests are mainly used to quantify the behaviour and strength of the instrument and to confirm simulation results. Here the movement applied to the instrument takes the form of an oscillation whose frequency increases with time and whose amplitude is calculated in such a way as to reproduce the forces to which the instrument must be able to resist. The randomized test is intended to be much more representative of what the instrument will undergo at launch.
  • Mechanical impact tests: the instrument is installed on an « impact table » equipped with pyrotechnic devices. These devices are like miniature cannons. The firing of a small explosive charge propels a metal mass that hits the table. The charge and metal mass are dimensioned to obtain a shock representative of what the instrument must withstand, for example when separating from the launcher or when opening the solar panels.
  • Thermal vacuum tests: the telescope is installed here in a tank in which vacuum is made. Various devices, liquid nitrogen-cooled screens and electric heaters allow to expose the instrument to the most extreme temperatures, hot or cold, that it will face in orbit.

The stress levels applied to the instruments during these tests are deliberately higher than those that will be experienced in flight. This makes it possible to cover both the uncertainties on the knowledge of the mechanical and thermal environment experienced throughout the mission and the manufacturing gaps between the STM models and the flight models.

The environmental tests of the STM models of the ECLAIRs and MXT telescopes were carried out at Airbus Defence & Space, which has all the necessary resources on the same technical platform. A CNES team of 30 people mobilized this summer by juggling the availability of test resources in order to be ready for the meeting scheduled with our Chinese partners. Everyone’s efforts have made it possible to achieve all the objectives set and to deliver the equipment on time.

Structural and Thermal Model of the ECLAIRs telescope

Structural and Thermal Model of the MXT telescope

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Author : Ph. Guillemot (CNES)
First results of the SVOM mission before launch !

First results of the SVOM mission before launch !

First results of the SVOM mission before launch !

Optical follow-up of gravitionnal waves

The first results of the space mission SVOM (for Space-based multi-band astronomical Variable Objects Monitor) have just been released before the launch scheduled for the end of 2021. How is this possible? Quite simply because this ambitious Franco-Chinese mission, which aims at studying gamma-ray bursts of the Universe, is also developing a network of ground-based cameras able to detect the emission of visible light that follows the outbreak of these bursts, the most violent known explosions. This network, dubbed Ground-based Wide Angle Camera (GWAC), is already in operation at the Xinglong Observatory in Northeast Beijing (China). Its test version, dubbed Mini-GWAC, successfully concluded a first campaign of monitoring and real-time follow-up of gravitational wave sources discovered by the LIGO (USA) and Virgo (Italy) facilities. These results are being published in the journal Research in Astronomy and Astrophysics.

See the luminous echo of a gravitational wave

The SVOM team has just published the results obtained by the Mini-GWAC instrument of the follow-up of the second sequence of gravitational wave detection (run O2) by LIGO and Virgo that took place from November 2016 to August 2017. Not less than 14 potential events were published by LIGO in this interval, eight of which were monitored by Mini-GWAC. Other six events were subsequently retracted by LIGO.
For two of them, the most spectacular, GW170104 and GW170608 which have been confirmed as resulting from the fusion of two black holes, optical tracking has worked remarkably well. In the case of GW170104 (for Gravitational Wave of January 04, 2017), it is the result of the merging of  two black holes of mass approximately 20 and 30 times that of the Sun.
Mini-GWAC was able to observe GW170104 a little more than 2 hours after the triggering of the alert and provide data for 10 hours, covering 62% of the error box. For GW170608 (June 8, 2018), nearly 20% of the region was covered. In both cases, no visible emission was detected, up to a magnitude of about mv = 12.

Left: Artist's impression of the fusion of two black holes producing a gravitational wave. Right: SVOM / Mini-GWAC exposure chart (yellow colored rectangles) covering the GW170104 wave error box. The color scale is a representation of the probability of the position of the source at the origin of the gravitational wave signal detected by LIGO. Credit @ SVOM

Left: Artist’s impression of the fusion of two black holes producing a gravitational wave. Right: SVOM / Mini-GWAC exposure chart (yellow colored rectangles) covering the GW170104 wave error box. The color scale is a representation of the probability of the position of the source at the origin of the gravitational wave signal detected by LIGO. Credit @ SVOM

The final version of the GWAC installation that was commissioned in late 2017 at the Xinglong Observatory (China) is now able to track gravitational wave alerts down to a visible magnitude mv = 16, more than 40 times fainter than the test version. In some cases, the emission of gravitational waves is also accompanied by gamma-ray bursts that will also be detected by the other SVOM instruments [1]. The entire GWAC device is now ready and able to detect the visible counterparts of these events, even before the launch of the SVOM mission.

[1] SVOM is a Franco-Chinese mission for the observation of the gamma-ray bursts of the Universe. Its  launch is currently scheduled for the end of 2021.
[2] GWAC is one of the components of the SVOM mission which also includes 4 instruments (ECLAIRs, MXT, GRM and VT) * which will be onboard the SVOM satellite. GWAC aims to complete observations from the ground to study and identify gamma-ray bursts detected from space by the SVOM satellite.
GWAC consists of 10 mounts each carrying 4 cameras of 18 cm in diameter and thus covering a total field of view of about 5000 square degrees. Each of the 40 cameras is equipped with a 4096 × 4096 E2V CCD operating in the 0.5 to 0.85 μm wavelength band with a field of view (FoV) of 150 deg². GWAC provides source locations up to a visible magnitude mv = 16 with an accuracy of 11 arcsec (for a 10 s exposure).
The preliminary Mini-GWAC test version consisted of a system of six mounts, each equipped with two cameras (Canon 85 / f1.2).

Deployment of GWAC robotic mounts at the Xinglong Observatory (China) for the search for counterparts in visible light of gamma bursts and gravitational waves. Each mount carries 4 cameras 18 cm in diameter and has a field of view of about 500 square degrees. The complete GWAC set covers a total field of view of 5000 square degrees. Copyrights NAOC / SVOM

Deployment of GWAC robotic mounts at the Xinglong Observatory (China) for the search for counterparts in visible light of gamma bursts and gravitational waves. Each mount carries 4 cameras 18 cm in diameter and has a field of view of about 500 square degrees. The complete GWAC set covers a total field of view of 5000 square degrees. Copyrights NAOC / SVOM


Publication :
« The mini-GWAC optical follow-up of the gravitational wave alerts.
Results from the O2 campaign and prospects for the upcoming O3 run. »
D. Turpin et al., Research in Astron. Astrophys. 2019 (in press), see  the publication in (PDF)

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Published on 2-Nov-2019
Author : bobi

Pierre Mandrou (1944-2019)

The SVOM family is in mourning

Pierre-Mandrou

Pierre at the Summer Palace, Beijing

Our friend and colleague Pierre Mandrou, astrophysicist at former CESR and now IRAP, passed away on Wednesday, September 27 at the age of 75, after a lucid and courageous fight against the disease.
Pierre has been an outstanding instrumental scientist in the domain of space gamma-ray astronomy, one of IRAP’s major scientific and technical expertises.
Since 1970, with his colleagues and friends at the CEA-Saclay, he has been working on the development of « spatialized » gamma-ray detectors. In particular, he was the scientific co-PI for the CNES SIGMA space telescope on board the Soviet GRANAT satellite. This pioneering mission made it possible to obtain the first high sensitivity and angular resolution mapping of the sky between 20 and 2000 keV, leading to the discovery of the « great annihilator » in the centre of our galaxy. He then worked as the « Instrument Scientist » of the CNES SPI telescope on ESA’s INTEGRAL satellite, another tremendous success, recently rewarded by the detection of the short gamma-ray burst associated with the gravitational wave source GW170817.
In recent years, he spent his energy on our SVOM project, of which he was scientific advisor. He was responsible for many contributions such as the impact of the South Atlantic Anomaly on the instruments or the definition of the mission’s pointing strategy. But for the SVOM family, Pierre will remain the father of the ECLAIRs telescope. He scientifically specified this instrument, dimensioned it and defined its overall properties.
For all those who had the chance to work with him, Pierre was and will remain a reference. We will remember his physical presence, his enthusiasm, his warm voice, his communicative skills and his great generosity.
The many testimonies we received attest Pierre’s influence and sympathy inside our community.

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Author : B. Cordier on behalf the SVOM collaboration
News 2019 April – the ECLAIRs and MXT calculators connect with the SVOM satellite for the first time

News 2019 April – the ECLAIRs and MXT calculators connect with the SVOM satellite for the first time

News 2019 April – the ECLAIRs and MXT calculators connect with the SVOM satellite for the first time

Category : news of the project

From mid-February to mid-March 2019, the Chinese and French SVOM project teams carried out the first coupling of the ECLAIRs and MXT instrument calculators with the SVOM satellite. The objective of these tests was to validate the electrical interfaces between the French equipment and the rest of the satellite.

On the French side, the ECLAIRs and MXT calculators are represented by their Engineering and Qualification Models (EQM). These models are, for their material part, fully representative of future flight models. On the other hand, the software part is limited to the command / control part interfaced with the satellite. At this stage, no science is implanted in the calculators. On the Chinese side, the satellite is represented by all the electronic boxes of the platform’s various equipment and payload, all assembled on a table, in a « Flat Sat » configuration.

SVOM Flat Sat with ECLAIRs (left) and MXT (right) boxes

SVOM Flat Sat with ECLAIRs (left) and MXT (right) boxes

The test sequence was carried out in two stages. In a first phase, the teams coupled the calculators electrically with the rest of the Flat Sat. During this step, all connectors, harnesses and electrical signals must be checked before gradually connecting the power supplies and then the various communication channels. At the end of this first phase, the French computers are connected to the satellite, powered by it and are able to communicate with the payload computer. The second phase can begin. The aim is to validate the proper functioning of the entire payload. Several test sequences are carried out to validate the different communication channels (Telemetry, remote controls and alert messages) and operational programming (Alert sequence, instrument mode management, South Atlantic Anomaly management, configuration table management).

This first meeting between Chinese and French equipment was also the opportunity to test the assembly of French boxes on the future satellite model used to qualify SVOM. This confirmed that the holes fall in front of the holes and that everything was properly installed.

Installation of the MXT box on the +Y wall of the SVOM QM payload module

Installation of the MXT box on the +Y wall of the SVOM QM Payload Module

 

Installation of the ECLAIRs box on the -Y wall of the SVOM QM payload module

Installation of the ECLAIRs box on the -Y wall of the SVOM QM Payload Module

 

SVOM QM Payload Module with MXT box (top left) and ECLAIRs box (bottom right)

SVOM QM Payload Module with MXT box (top left) and ECLAIRs box (bottom right)

At the end of one month of activity, the results of this first campaign of Franco-Chinese activities are very positive. From a technical point of view, all the objectives have been achieved. On a more human level, these first activities made it possible to define a common basis of work that was respectful of the cultures of the two teams, in a spirit that was always positive and constructive.

Franco-Chinese integration team in front of the Payload Module (QM)

Franco-Chinese integration team in front of the Payload Module (QM)

 

Handover in Shanghai between the two French integration teams

Handover in Shanghai between the two French integration teams

Rendez-vous now at the beginning of the summer to continue the activities with the arrival of the mechanical and thermal models of the 2 instruments ECLAIRs and MXT, their integration on the satellite and the environmental test campaign.

Infos

Author : Ph. Guillemot (CNES)
Looking back: Unchanging and transient skies

Looking back: Unchanging and transient skies

Looking back: Unchanging and transient skies

The combination of two worldviews

In the past, Europe and China have had two radically different visions of the cosmos. While the former has long thought of the fixed and immutable sky as revealing only silent perfection, the latter has, on the contrary, relentlessly tracked down the slightest celestial changes, sometimes almost imperceptible phenomena, betrayed only by infinitesimal manifestations. Unchanging sky or transient sky therefore remained for a long time two opposing visions. Today the transient sky has become an irreplaceable source of information for astrophysicists and China and Europe are joining forces to unlock the secrets of this constantly changing world where some cataclysms can occur in just a few fractions of a second.

The SVOM (Space-based multi-band Variable Objects Monitor) space mission, to be launched in 2021, will be the second Sino-French scientific mission from space after the launch of CFOSAT (China-France Oceanography SATellite) on 29 October 2018. Its purpose is to detect the brutal sudden end of the very first stars, located at the edge of the Universe, and also to help locate super-powerful cosmic phenomena generated by the fusion of compact stars. This is an undeniable tribute to the long Chinese tradition.

Unchanging sky and transient sky

Europe, and more broadly the Mediterranean basin, has mainly received its astronomical tradition from the ancient Greek world. From an often very limited and superficial observation of the heavens, the ancient Greek thinkers had imagined a cosmic world divided into two distinct domains. On the one hand, the sub-lunar world close to the Earth where all the changing cosmic phenomena (meteors, comets,…) were confined and on the other hand the supra-lunar world where the errant bodies that are the planets orbit in perfect circles. This world itself was entirely contained in a last celestial sphere, the fixed, immutable and eternal sphere that carried the stars. In this highly idealized vision, it was therefore impossible to think of discovering any change whatsoever in this last starred sphere, which, according to common experience, indeed seemed largely untroubled.

After the collapse of classical Greek culture at the beginning of the modern era, this same idealized vision was taken up by the two monotheistic religions, Christianity and Islam, which were to develop in turn. This time, the perfect and immutable character of the heavens was no longer a aesthetic vision from philosophical thinkers, but became a strict religious prescription that sought to describe the perfection of the great Creator. To identify elements that could question this cosmic perfection then became a frontal opposition to the religious powers that also dominated the political world of the time. This religious dogma has thus acted for nearly 1500 years on astronomical science in Europe.

The conception of the perfect and unchanging sky

The conception of the perfect and unchanging sky in Europe for more than 1500 years is symbolized by this representation of the celestial spheres made in 1549 by the French mathematician-astronomer Oronce Fine. In this conception of the universe, the Earth is at the centre and each sphere carries the different planets and the Sun. The last sphere is that of the stars, which remains totally unaltered.

In contrast, other parts of the world have not been subjected to this religious censorship, and in the case of China, on the contrary, it was the political power itself that has favoured since the dawn of time, the deep examination of the changing sky, permanently scanning the heavens in search of transitional phenomena.
In a premonitory way, China is the civilization that has given the most importance to the changes in the skies. At the origin of this quest, the permanent concern to preserve the harmony between Earth and Heaven. The two terrestrial and celestial worlds were seen as two complementary worlds in constant interaction and any disruption of balance in the sky heralded a similar disruption on Earth that needed to be identified. In this vision of Heaven as a mirror of the Earth, the main role was assigned to the sovereign himself, called « Son of Heaven » (Tianzi), because his essential responsibility was to guarantee this Earth-Sky harmony. The Chinese emperor did not receive his mandate and legitimacy from a simple family line or even a conquest, but above all he had to justify a « celestial mandate » (Tianming) granted to him if he could predict and anticipate astronomical phenomena. In this sense, China is the only country in the world to have elevated astronomy to the rank of state science.

The representation of the sky in ancient China

The representation of the sky in ancient China places the celestial emperor in the center, at the position of the celestial pole. The Chinese sky is divided into five palaces: the central palace around the North Pole and the 4 palaces along the celestial equator corresponding to the four geographical directions, associated with the four mythical animals. The many constellations (more than 300) are all associated with elements of the empire. Heaven is conceived as a mirror of the terrestrial Empire. © N. Mistry/O. Hodasava

On the orders of the emperor and the central power, everything that could disturb the harmony of the heavens was hunted down, discovered and interpreted. Entire bodies of astronomers and astrologers were mobilized night after night in imperial astronomical observatories gathering hundreds of people (observers, timekeepers and clepsydra, calendar specialists, mathematicians,…) who had nothing to envy our great modern scientific institutes.
From the beginning of the Hans, in the second century BC, the specifications were clearly established and reported to us by the great historian-astronomer of ancient China, Sima Qian, in his encyclopedic work « The Historical Memories »: « If in the whole cycle from beginning to end and from antiquity to modern times the changes that occur at fixed times have been observed deeply and if we have examined their details and the whole, then the science of the Governors of Heaven is complete. « Shiji, Historical Memoirs of Astronomer Historian Sima Qian (109 to 91 BCE).

Historian and astronomer Sima Qian

Historian and astronomer Sima Qian (from 144 to 85 BC), author of the first major Chinese historical encyclopedia.

This perfect organization, which has covered more than forty centuries of Chinese civilization, has provided the world with fundamental astronomical discoveries, often still greatly underestimated.
The existence of sunspots on the Sun’s surface was thus clearly established as early as the Hans dynasty (206 BCE to 220 CE) while their discovery in Europe is attributed to Galileo (1613 CE). Even more spectacularly, the first mention of a star explosion, resulting in the temporary appearance of a new star (novae or supernovae), seems to have been documented in China as early as the 15th century BC and precise catalogues and reports of these spectacular events are available since the Han period. In Europe, the first description of such phenomena was given only by the Danish astronomer Tycho Brahe in 1573.

One of the accounts of the Song dynasty describing the appearance of the Crab supernova

One of the accounts of the Song dynasty describing the appearance of the Crab supernova. The text is taken from the chronicle « Essential of Song History ». It describes, under the reign of Emperor Renzong, the appearance of a new star as bright as Venus, which remained visible during the day for 23 days.
It reads (from top to bottom and from right to left, highlighted in red): « In the first year of the Jiayou reign, in the third lunar month[from 19 March to 17 April 1056], the head of the Astronomy Bureau said: « The invited star has disappeared, which is a sign of the host’s departure. » Earlier, during the 5th month of the first year of the Zhihe reign[July 1054], this star had appeared in the East, guarding Tianguan[天关- the star ζ Tauri]. She was visible during the day as Venus. It pointed its rays in all directions and its color was pale red. It remained visible[during the day] for 23 days. ». Crab supernova remanent, X-ray image composition, visible and infrared light. Credit: X-ray: NASA/CXC/SAO/F.Seward; Optical: NASA/ESA/ASU/ASU/J.Hester & A.Loll; Infrared: NASA/JPL-Caltech/Univ. Minn./R.Gehrz.

Today, modern astronomers know that everything that changes in the sky reveals the most extraordinary cosmic phenomena.
Thus the appearance of a supernovae, a new transitional star, reveals an event that is crucial to the history of the universe: the explosion of a massive star that will spread in space all the complex cosmic elements (carbon, nitrogen, oxygen, etc.) produced in the star’s heart that can contribute later to the emergence of life on a planet.
In other areas of light such as gamma rays, the appearance of very short bursts of gamma radiation also marks the end of life of very large stars, which can be detected thanks to this signal up to the far limits of the Universe.
Finally, beyond light itself, the very structure of space-time can be transiently altered by the monstrous fusion of black holes or compact stars and reach us as gravitational waves, new messengers now detectable on Earth by laser-based sensors. In short, we are learning much more today from the transient sky than from the permanent sky
All these transient phenomena are the main objectives of the Franco-Chinese SVOM mission. Their detection, location and precise description will be recorded to better interpret the sky, just as the astronomers of the Han dynasty did more than 2000 years ago. Thus the same concern to better read the changes in Heaven, a quest shared today by China and France thanks to SVOM, is renewed centuries later.

References

Jean-Marc Bonnet-Bidaud, « 4000 ans d’astronomie chinoise », Ed. Belin, 2017.
Joseph Needham and Wang Ling. « Science and Civilisation in China, vol. 3, Mathematics and the Sciences of the Heavens and the Earth », Cambridge University Press, 1959.
Xiaochun Sun and Jacob Kistemaker, « The Chinese Sky during the Han – Constellating Stars & Society », Ed. Brill, 1997.
Zezong Xi, Shuren Bo, « Ancient Oriental Records of Novae and Supernovæ », Science, vol. 154, p. 597, 1965.

Infos

Author : Jean-Marc Bonnet-Bidaud
First light on the MXT camera

First light on the MXT camera

First light on the MXT camera

At the end of August, the first X-ray photons were detected with a prototype of the focal plane of the MXT camera (the engineering model). This is an important step in validating the design of the detection chain.
The design of the MXT camera began in 2014. It contains a pixelated silicon detector of pnCCD type with 256×256 pixels, similar to the one integrated in the eRosita instrument of the Russian Spectrum-Röntgen Gamma (SRG) satellite to be launched next year.
The X-ray detector and its front-end electronics are mounted on a multilayer ceramic circuit to ensure good thermal dissipation. This set, called the focal plane, was placed in a cryostat to allow laboratory tests to validate the operation of the detection chain at the target operating temperature of -65°C.
The integration of the focal plane into the clean room cryostat involves several complex steps, which required great rigour and several repetitions, as shown in the video below.

Once the cryostat was closed, the detector was then cooled to -60°C and illuminated with a Cobalt-57 radioactive source. Tests carried out at the end of August showed that it correctly detects X-ray photons, thus validating all the work carried out by the various teams over the past 4 years.

First detected X-ray photons. Cobalt-57 source, -60°C, actual acquisition rate.

Each event (point on the image) represents the detection of a photon from the source by the focal plane. By extracting the energy deposited in the detector for each impact, a spectrum can be constructed. The following figure represents the first spectrum obtained on a Cobalt-57 source by the prototype of the MXT focal plane. The Cobalt-57 low energy lines at 6.4 keV, 7 keV and 14 keV are recognized in this spectrum.

First measured X-ray spectrum, 57Co source, -50°C

First measured X-ray spectrum, Cobalt-57 source, -50°C

Next Steps
The next step, in early 2019, will be to irradiate this prototype of the focal plane with protons to simulate space conditions.
In one year, the flight model of the focal plane will be integrated into the flight model of the camera.

The CEA Irfu is in charge of the design and construction of the X-ray camera of the MXT telescope.

Gravitational waves in the spotlight in Les Houches

Gravitational waves in the spotlight in Les Houches

Gravitational waves in the spotlight in Les Houches

The third SVOM scientific workshop, entitled « Disentangling the merging Universe with SVOM » and bringing together 70 participants, was held from 14 to 18 May 2018 at the Houches physics school in the Chamonix valley. This year, a scientific theme was particularly highlighted, the contribution of the SVOM mission to the study of gravitational waves at the dawn of the next decade. The observation strategy during a gravitational wave warning was at the heart of the debates.

This workshop, organized by a committee of Sino-French scientists, gathered 70 participants and was hosted in the very friendly School of Physics of Houches.

This workshop, organized by a committee of Sino-French scientists, gathered 70 participants and was hosted in the very friendly School of Physics of Houches.

On August 17, 2017 the Ligo-Virgo collaboration detected a packet of gravitational waves from the fusion of two neutron stars lurking in the galaxy NGC 4993. Less than two seconds later, the Gamma ray Burst Monitor (GBM) of the Fermi mission detected for the first time an electromagnetic counterpart to this event, a signal confirmed by the Integral satellite. This correlated detection in gravitational waves and electromagnetic waves is a major scientific fact of the last decade. The SVOM mission, whose primary objective is the detection and study of gamma-ray bursts, is particularly well suited to contribute to this major scientific theme in view of its array of instruments equipping its space platform and the ground resources at its disposal.

During this workshop, several sessions described the state of the art of gravitational wave detection by active detectors, in terms of scientific results and future projections. The event of 17 August 2017 (fusion of two neutron stars) was the subject of special attention. The potential of the SVOM mission was highlighted, informed by simulations of the detection of such an event by the mission instruments and their contribution to the community.

Beyond this theme, the scientists exchanged on the more practical aspects of the technical constraints of the mission (orbit, accessible sky zone in accordance with the main program, opportunity and limit of modification of the satellite point linked to an alert, etc.).

The participants also took advantage of the majestic setting of the Houches School of Physics to address new research themes and update and complete the scientific document describing the mission in a broad sense (the White Paper).

 

The presentations made by the participants took place in a magnificent setting where a tea tasting was organized.

The presentations made by the participants took place in a magnificent setting where a tea tasting was organized.

News 2017 October – mid-phase C review of the SVOM mission

The mid-phase C review named System Interface Review (SIR) was held in Xi’an from October 16 to 19, 2017 in Shaanxi Province.

Figure 1: Group photo of the mid-phase C review. The meeting was held in Xi'an from October 16th to 19th, 2017. This review brought together around hundred people.

Figure 1: Group photo of the mid-phase C review. The meeting was held in Xi’an from October 16th to 19th, 2017. This review brought together around hundred people.

The purpose of this review was to freeze the definition of all the « system » interfaces schematized by the arrows in Figure 2 and to begin to define the organization and content of the « system » tests. For example, the satellite reprogramming loop in case of an opportunity target request was discussed in detail. This review was addressed mainly to a group of French-Chinese experts, chosen for their expertise in the conduct of a space project (ground segment specialists, antennas network specialists …)

 Figure 2: Schematic diagram of the "system" of the SVOM mission showing the main entities and their interfaces symbolized by the arrows.


Figure 2: Schematic diagram of the « system » of the SVOM mission showing the main entities and their interfaces symbolized by the arrows.

The Project presentations made by the SVOM consortium members were spread over a day and a half. Following these presentations, the group of experts formulated 79 questions. The following day, the SVOM teams responded in detail to the raised points. The end of the review resulted in the group report. The review group was pleased with the work done since the Preliminary Design Review (PDR) last year in June. He appreciated the quality of the presentations and the answers to the questions. In his preliminary conclusion, he considers this review to be successful.

The next review, Critical Design Review, will close Phase C. It is scheduled for spring 2019

Recall below the different phases of a space project:
• phase 0: mission analysis
• Phase A: feasibility study, closed by the Preliminary Requirements Review (PRR)
• Phase B: preliminary design, completed by the Preliminary Design Review (PDR)
• Phase C: Detailed Design, closed by the Critical Design Review (CDR)
• phase D: realization, qualification
• phase E: exploitation

 

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Author : CEA-Irfu

SVOM in the era of gravitational waves

The event of August 2017

On August 17, 2017, ground-based gravitational wave detectors (LIGO and Virgo) detected an event, called GW 170817, interpreted as the fusion of two neutron stars. This is the first time that LIGO detects a signal whose profile is similar to the fusion of two neutron stars, but what made the event even more unique is the temporal and spatial coincident detection of a short gamma burst GRB170817A by the GBM detector onboard the Fermi satellite. The detection was confirmed and announced in the following minutes by the SPI spectrometer onboard the INTEGRAL satellite.

The characteristics of GRB170817A were published after a few hours on the site of the Fermi / GBM mission. This is a low-intensity short gamma burst lasting about 2 seconds. Taking into account the distance estimated by the gravitational wave analyses, as well as its observed flux, GRB 170817A is an unusual burst, particularly sub-luminous (see Figure 1). It could be a gamma burst seen from the side.

Figure 1: GRB 170817A located on the radiated energy (Eiso) diagram according to the redshift (distance indicator). This diagram is constructed from a sample of bursts with well-measured spectral parameters. GRB 980425 is the longest known longest burst.

Figure 1: GRB 170817A located on the radiated energy (Eiso) diagram according to the redshift (distance indicator). This diagram is constructed from a sample of bursts with well-measured spectral parameters. GRB 980425 is the longest known longest burst.

An unprecedented observational campaign followed, mobilizing dozens of observatories on Earth and in space to detect and characterize the electromagnetic counterpart of the gravitational wave source. Thanks to the contribution of Virgo, the error circle was considerably reduced which allowed a fast tracking on the ground by small telescopes. By selecting galaxies located at the distance deduced from the gravitational signal, the 1 m Swope telescope at the Las Campanas observatory detected a new source SSS17A near the galaxy NGC 4993 at 40 Mpc. In the hours that followed other telescopes (DLT 40, Vista, Master, DECam, LCOGT) confirmed this detection, motivating the whole community to focus on SSS17A and leading to the detection of the electromagnetic counterpart of GW 170817 in all the wavelengths of the ultraviolet to the radio domain. This unprecedented campaign was rewarded by the discovery of a kilonova [1].

The succession of observations that have made the detection and localisation of the electromagnetic counterparts of GW 170817 possible reinforces the observational strategy chosen for the SVOM mission. With its set of interconnected multi-wavelength detectors, covering the electromagnetic spectrum from gamma rays to infra-red, SVOM will be able to detect and study these gravitational wave sources resulting from the fusion of two neutron stars and producing short bursts.

What would have SVOM seen if the mission had been online on the 17th of August 2017 ?

If the burst had appeared in the field of view of its high-energy detectors (ECLAIRs and GRM), SVOM would have detected it with a high probability and would have sent a trigger warning to the ground (see figure 2), all the while measuring the energy emitted in gamma rays. At the same time, the satellite would have slewed automatically to put the burst in the center of the field of view of its X-ray and optical instruments (MXT and VT), initiating an observing sequence of several hours. The optical counterpart of GW 170817, the emission produced by the kilonova associated with the fusion of the two neutron stars, would have been easily detected by the visible telescope VT [2] (see Figure 3).

Figure 2: Significance of the GRB 170817A detection by the ECLAIRs and GRM instruments according to the angle between the GRB and the optical axis of ECLAIRs. Horizontal lines indicate trigger thresholds; in red for slewing the satellite, in black for sending an alert to the ground.

Figure 2: Significance of the GRB 170817A detection by the ECLAIRs and GRM instruments according to the angle between the GRB and the optical axis of ECLAIRs. Horizontal lines indicate trigger thresholds; in red for slewing the satellite, in black for sending an alert to the ground.

But what would SVOM have seen if GRB170817A had not been in the field of view of its high-energy instruments (ECLAIRs and GRM) ?

Upon receiving the LIGO-Virgo alert at the French scientific center, SVOM would have triggered its robotic telescopes (F-GFT and C-GFT). By selecting nearby galaxies compatible with the probable distance from the event and contained in the gravitational wave detector error circle, SVOM’s robotic telescopes would have started a systematic search for the optical counterpart by performing several observation cycles. This strategy is particularly suited for the discovery of transient objects in their brightening phase. Thanks to its sensitivity but also thanks to its infra-red capabilities, the French GFT would certainly have detected the kilonova associated with GW 170817 (see figure 3).

Figure 3: The kilonova light curve associated with GW 170817 with respect to VT and F-GFT sensitivity. Simulation of a VT image corresponding to an exposure of 300s at the maximum brightness of the kilonova.

Figure 3: The kilonova light curve associated with GW 170817 with respect to VT and F-GFT sensitivity. Simulation of a VT image corresponding to an exposure of 300s at the maximum brightness of the kilonova.

In parallel, the French scientific center would have prepared a request for a multi-messenger opportunity target, asking the satellite to interrupt its observing sequence and point at various regions of the sky within the error circle of the gravitational wave detectors. It typically takes about ten hours to reprogram the satellite. Although arriving later, the VT would have easily detected the kilonova associated with the fusion of the two neutron stars (see Figure 3).

And now ?

In the beginning of the next decade, thanks to its ground and space-based instruments, the SVOM mission will certainly be a major player in the study of the transient sky and should significantly contribute to the study of gravitational wave sources. Starting next year, some of the SVOM ground-based telescopes (GWAC) should be operational and should validate the strategies implemented within the consortium at the next LIGO-Virgo data collection scheduled for autumn 2018.

 

[1] Kilonova: during the coalescence of two neutron stars, neutron-rich material is suddenly released under temperature and density conditions very favorable for the nucleosynthesis of heavy elements by the fast neutron capture process (process r). This is expected to result in the quasi-isotropic ejection of heavy-element-enriched material. This material is heated by the radioactivity of freshly synthesised elements and radiate thermally, with a color evolution from blue to red due to progressive cooling. This emission called kilonova has a physical origin quite distinct from the gamma ray burst and its afterglow.

[2] For this event no short-term X-ray observations occurred. It is therefore difficult to predict a possible detection by the MXT X-ray telescope, despite the fact that it is expected by various models.

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Author : CEA-Irfu & Jesse Palmerio
Stéphane Basa presents the French robotic telescope

Stéphane Basa presents the French robotic telescope

Stéphane Basa presents the French robotic telescope

Meeting with Stéphane Basa, who presents the French robotic telescope F-GFT.

Click on CC to activate the English subtitle

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Author : CEA-Irfu
SVOM/mini-GWAC, a fast response to the third gravitational wave event

SVOM/mini-GWAC, a fast response to the third gravitational wave event

SVOM/mini-GWAC, a fast response to the third gravitational wave event

The third gravitational wave event (GW170104) discovered by the LIGO-Virgo collaboration confirms the existence of massive stellar black holes with a mass larger than 20 solar masses. These two in-orbit stellar masses stars finally merged to form a compact object of nearly 50 solar masses. During this process, a huge amount of gravitational wave, predicted by the general relativity theory, is emitted. This is precisely the signal of this fusion that the two LIGO interferometers detected on earth for the third time.

Searching for an electromagnetic counterpart to such event is today a challenge, both on a observational side or on a theoretical aspect. Many multi-wavelength networks, on ground and in space, share this goal. Among them, the SVOM mission has started to survey the GW candidates with a dedicated instrument, the SVOM/mini-GWAC equipment, pathfinder towards a more complete SVOM instrument. Starting just a few hours after the communication to the scientific community of the GW position, the following text describes the different steps of this search.

The SVOM/mini-GWAC system located on the Xinglong site in China covers a total field of view of 5000 square degrees. It is composed by 6 mounts on which are arranged two cameras (Canon 85 / f1.2). Mini-GWAC scans the sky every night in search of transient sources using its real-time algorithms with a limiting magnitude of 12 for an exposure time of 15s. Each significant detection is automatically followed by two 60 cm robotic telescopes to better characterize the candidate.

The SVOM/mini-GWAC system located on the Xinglong site in China covers a total field of view of 5000 square degrees. It is composed by 6 mounts on which are arranged two cameras (Canon 85 / f1.2). Mini-GWAC scans the sky every night in search of transient sources using its real-time algorithms with a limiting magnitude of 12 for an exposure time of 15s. Each significant detection is automatically followed by two 60 cm robotic telescopes to better characterize the candidate. Credit@NAOC

GW170104

The gravitational wave event GW170104 has been detected on 4 January 2017 at 10:11:58 UTC by the LIGO-Virgo consortium with the twin advanced interferometers Hanford and Livingston located in the United States.
This event is the result of the coalescence of a pair of stellar-mass black holes with respectively 31.2(+8.4;−6.0) and 19.4 (+5.3;−5.9) solar masses. The source luminosity distance is 880 (+450;−390)  Mpc corresponding to a redshift of z=0.18 (+0.08;−0.07). The signal was measured with a signal-to-noise ratio of 13 and a false alarm rate less than 1 in 70 000 years.

Timeline and Localization error box

The GW alert has been delivered to the astronomical community with a delay of 6.3 h.
The initial 90% localization error box covers an area on the sky of 2065 deg2.
An update of the localization error box has been delivered 4 months later with a 22% reduction of the localization error box.

SVOM activity

As soon as the GW alert was delivered to the astronomical community (6h after the trigger time e.g 4 hours after the beginning of the Chinese night), the probability skymap was quickly digested in order to produce the follow-up observation plan.
The mini-GWAC telescopes covered 80% of the error box in 14exposures of variable duration between 1 and 3 hours.
The SVOM group reported their follow-up observations in a circular published at the end of the night.
SVOM/Mini-GWAC follow-up observations were unique in the optical band: SVOM/mini-GWAC performed the largest probability coverage of GW170401 localization in shortest latency for optical band.

The SVOM/mini-GWAC exposer map (yellow boxes) superimposed over the GW170104 error box. The color scale represents the Bayesian probability that the source at the origin of the GW signal is at a given location on the sky.

The SVOM/mini-GWAC exposer map (yellow boxes) superimposed over the GW170104 error box. The color scale represents the Bayesian probability that the source at the origin of the GW signal is at a given location on the sky. Credit@SVOM

At this time, we didn’t detect a relevant electromagnetic counterpart but for the future, we look forward the whole GWAC system (limit mag 16), in operation at fall 2017.
SVOM science is on the way !

The multi-messenger SVOM team in front of the GWAC system. This upgraded version of the mini-GWAC equipment, with a sensitivity limit of 16 magnitude, will be in in operation in fall 2017.

The multi-messenger SVOM team in front of the GWAC system. This upgraded version of the mini-GWAC equipment, with a sensitivity limit of 16 magnitude, will be in in operation in fall 2017. Credit@SVOM

 

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Author : CEA-Irfu
Second workshop in China

Second workshop in China

Second workshop in China

After the one holds in Les Houches in April 2016, the second scientific workshop of SVOM mission took place from 24 to 28 April 2017 at Qiannan inside the province of Guizhou located in the south of China. Called Surveying the Fast Changing Multi-wavelength Sky with SVOM”, this meeting gathered almost 90 participants on a site near the new giant radio telescope FAST.

More than 90 scientist gathered in the Guizhou province for the second scientific workshop of SVOM.

More than 90 scientist gathered in the Guizhou province for the second scientific workshop of SVOM.

The new generation of observatory instruments accessible today for the scientific community allow a sky survey, not only for all the color or wavelength but also for non-photonic windows with neutrinos or gravitational waves. The abundance and the quality of observatory tools in space as well as on the ground put this astrophysics, called multi-messenger astrophysics, in a golden age. It provides access to information on the physics of emitter object but also explore the Universe until considerable distances, opening opportunities towards cosmological studies.

Within this context, several main topics were covered throughout the workshop: gamma ray-burst (type of progenitor, cosmological probe), gravitational waves (formation of massive stellar black holes and their evolution over the universe history), neutrinos (type of sources, link with gamma ray-burst and high energy cosmic rays) and fast radio burst FRB (mechanisms involved, survey of intergalactic medium).
At each stage, theoretical and observational talks allow to review the state of the art and to trigger scientific debates. The role of SVOM in this scientific overview was the core of several scientific sessions.
During this workshop, a visit of the giant telescope FAST inaugurated in September 2016 was planned.
Located in a region with particular landscape, this instrument is the jewel of the Chinese radio astronomy.

The five hundred Aperture Spherical radio Telescope FAST is located inside a natural basin in the southern Guizhou province.

The five hundred Aperture Spherical radio Telescope FAST is located inside a natural basin in the southern Guizhou province.

The schedule and the presentation of this workshop are accessible here.
The next workshop will be held in France from 13 to 18 May 2018 in the Ecole de Physique des Houches located in Chamonix valley.

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Author : CEA-Irfu

Neil Gehrels (1952 – 2017)

The passing of Neil Gerhels on Monday the 6th of February 2017 is an immense loss for our scientific community. We have lost not only a great scientist and our best ambassador, but also a friend. Neil has helped us build the SVOM mission and has always shown unwavering support.

Neil during hisprésentation « Overview of the Swift results, advice for SVOM » at the scientific workshop of SVOM in April 2016.

Amidst all his qualities, Neil was a first and foremost a visionary who showed us the path of the time domain astronomy. He will be remembered as an example for many generations of scientists, and in particular our youngest ones.

With every new burst we think of him, we miss him already…

 

Infos

Author : B. Cordier on behalf of the SVOM collaboration

News 2016 July – End of phase B of the SVOM mission

Catégorie : Nouvelles du projet

La revue de fin de phase B nommée PDR (Preliminary Design Review), l’une des étapes clé dans la conduite d’un projet spatial, s’est tenue du 4 au 6 juillet 2016 à Yantai dans la province du Shandong.

Photo de groupe PDR 2016

Photo de groupe de la revue de fin de phase B qui s’est tenue à Yantai en juillet 2016 et a rassemblé une centaine de participants.

L’objectif de cette revue était de s’assurer que l’ensemble du « système » proposé pour la mission SVOM répond aux exigences scientifiques. Elle s’adressait principalement à un groupe de revue, une entité composée de personnes extérieures au projet et choisies pour leur compétence dans la conduite d’un projet spatial.

Les présentations du projet par les membres du consortium SVOM étaient réparties sur un jour et demi. Suite à ces exposés, le groupe de revue a formulé 123 questions. La journée suivante, les équipes SVOM ont répondu en détails aux points soulevés par le groupe de revue. La fin de la revue s’est soldée par le rapport du groupe.
Le groupe de revue a été satisfait de l’avancée des travaux réalisés depuis la System Requirement Review (SRR) l’an dernier. Il a apprécié la documentation approfondie, la qualité des présentations et les réponses aux questions. Dans sa conclusion préliminaire il recommande que la mission SVOM passe en phase C sans réserve.
La prochaine revue, Critical Design Review, clôturera la Phase C, Elle est prévue pour l’été 2018.

Rappellons ci-après les Différentes phases d’un projet spatial :

  • la phase 0 : analyse de mission [mission analysis]
  • la phase A : étude de faisabilité (feasibility study), cloturée par la Revue des Exigences Préliminaires (Préliminary Requirement Review)
  • la phase B : définition préliminaire (preliminary design), clôturée par la Revue de définition préliminaire (Preliminary Design Review)
  • la phase C : définition détaillée (detailed design), clôturée par la revue de définition détaillée (Critical Design Review)
  • la phase D : réalisation, qualification
  • la phase E : exploitation

 

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Published on 07/14/2016
Author : CEA-Irfu
Vibration test on the first prototype of ECLAIRs coded mask

Vibration test on the first prototype of ECLAIRs coded mask

Vibration test on the first prototype of ECLAIRs coded mask

The first prototype of the ECLAIRs coded mask has been tested in vibration at the PIT of Saint-Quentin-en-Yvelines.

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Published on 07/25/2016
Author : Cyril Lachaud
Machining an aluminium prototype of ECLAIRs coded mask

Machining an aluminium prototype of ECLAIRs coded mask

Machining an aluminium prototype of ECLAIRs coded mask

The ECLAIRs coded mask development activities required the processing of an aluminium coded mask prototype to perform mechanical stress tests. The processing of a sandwich of 5 aluminium foils (0.5mm thickness) was done with a water jet machine at the TechShop Leroy Merlin of Ivry sur Seine, the 10th may 2016.

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Published on 07/22/2016
Author : Bertrand Cordier
SVOM, from Les Houches to the white paper

SVOM, from Les Houches to the white paper

SVOM, from Les Houches to the white paper

As part of the preparation of SVOM mission, a scientific workshop from 10 to 15 April 2016 at Ecole de Physique des Houches in the Chamonix valley, called « The Deep and Transient Universe in the SVOM Era: New Challenges and Opportunities ».

This workshop aimed to gather the scientific community (Chinese and French) interested in the project. Although the study of gamma ray burst remains a main goal of the mission, the time dedicated to targets of opportunity will grow up like we noticed for the Swift mission. And thus, SVOM is also a multi wavelength mission devoted to the study of the transient sky. The subjects discussed were very diverse: gamma ray burst, Galactic X-ray binary, active galactic nuclei or even the distant Universe. Research of messengers that are non-photonic like gravitational waves or neutrinos were also discussed during the workshop.

It also allowed the participants to put the bases of a white paper. This document is going to be presented during the end-of-phase B review, which will take place in China in July 2016. It will provide a work basis to the scientific community interested in the SVOM mission. Gathering more than 70 participants, mostly Chinese and French, the workshop was an opportunity to develop contacts and dialogues in the country setting of the Ecole de Physique des Houches.

The schedule and the presentations of the workshop are available here.

This workshop, organized by a committee of Sino-French scientists gathered 70 participants and was hold in the country setting and friendly site of Ecole de Physique des Houches. It was also the moment to present the beauty of the Chamonix valley during a sunny afternoon. (@CEA)

This workshop, organized by a committee of Sino-French scientists gathered 70 participants and was hold in the country setting and friendly site of Ecole de Physique des Houches. It was also the moment to present the beauty of the Chamonix valley during a sunny afternoon. (@CEA)

This meeting was the first one of a series of yearly appointment open to the community. The next one is planned in April/May 2017 in the province of Guizhou in China near the giant radio telescope FAST presently under construction.

Consult the white paper prepared following this workshop: The Deep and Transient Universe in the SVOM Era: New Challenges and Opportunities – Scientific prospects of the SVOM mission (2016 edition)

Infos

Author : CEA-Irfu

News 2016 March

Presentation of two development models of the SVOM satellite

Category: news of the project

A meeting on the advancement of the SVOM project took place from 21 to 25 March 2016 in Shanghai inside the building of SECM (Shanghai Engineering Center for Microsatellites). One of the aim of this assembly was the preparation of the end-of-phase B review, which will be held from July 4 to July 8 in Yantai, in the Shandong province.

secm-photo-groupe

This meeting was also an opportunity to check the numerous advancement and more particularly the realization of two models of development of the SVOM satellite: the structural and thermal model (STM) and the electric model (EM), both presentated to the French team.

secm-photo-stm-em

 

Video of the STM: in this video of the structural and thermal model, we recognize the model of the platform with its solar panels here folded (in blue) and the model of the payload with its scientific instruments (VT, MXT, ECLAIRs). The set will be integrated in April 2016 then placed inside a vacuum chamber of the SECM. A phase of thermal tests will begin for one month.

Video of EM: In this video of the electrical model, we recognize the different units of the platform in particular those of the altitude control system, the stellar sensor and the magnetic torquers.

Glossary :

  • STM (Structural and thermal model): model developed to predict the structural and thermal behavior of an object
  • EM (electrical model): model to test the functional and electric behavior and audit the absence of interferences between different Equipment.

 

Infos

Published on 03/31/2016
Author : CEA-Irfu
Alain Klotz presents the  TAROT telescope

Alain Klotz presents the TAROT telescope

Alain Klotz presents the TAROT telescope

Meeting with Alain Klotz, who presents us the TAROT telescope.

Côte d’Azur observatory located in the Plateau de Calern, August 2015.

Click on CC to activate the English subtitle

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Published on 08/24/2015
The ECLAIRs coded mask

The ECLAIRs coded mask

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The ECLAIRs coded mask

GRBs appear randomly in the sky. Therefore detecting a large fraction of them requires to design wide-field instruments. ECLAIRs has been designed to ensure both the detection of  GRBs with the best possible sensitivity and the distribution of their sky position with the best possible accuracy. Following a detection, the spacecraft will slew in order to repoint the narrow-field instruments in the direction of the burst. Creating wide-field optics focussing hard X-rays and Gamma-rays is currently out of reach. Thus, the instrument ECLAIRs is based on the coded mask technic.

Coding the sky light

The coded mask technic has been used for decades in Gamma-/X-ray astronomy as it is a robust and efficient way to localize high energy sources over a wide field of view. A coded mask is made of opaque and transparent elements in a given energy range arranged in a particular pattern. The mask is placed above a pixellized detection plane. The light from each source within the camera field of view will then project a unique shadow of the mask on the detection plane, therefore coding the sky light. By measuring this shadow and using deconvolution technics, it is possible to retrieve the position of any source within the camera field of view.

 

Prototype masque

Prototype of the ECLAIRs coded mask. Credits: IRFU/CEA

For bright sources, the mask pattern in the projected shadow could be seen easily. However for faint sources, we need to rely on mathematical tools.  For the faintest sources, it will not be possible to distinguish the source from the background. It means that the camera reaches its limiting sensitivity.

Another striking aspect of using coded mask technics is the case for the presence of multiple sources within the field of view. Deconvolution technics enable us to decipher the direction of any incident photons forming the shadow on the detection plane. It is then possible for instance to say if a third of them comes from a burst, another third from the background and the last part from another source. Thanks to this, it is possible to build a sky image with all the sources present within the field of view.

Encoding key

In order to reconstruct a sky image using deconvolution algorithm, we need to know what encoding key has been used in the first place to code the signal. The coding of the data relies on multiplexing (i.e. transforming/re-arranging) multiple sources of signal in one signal using a particular encoding key. Then these coded data could be transmitted. Once received, the original signals could be retrieved using demultiplexing technics and the same encoding key. Such technics are often used in telecommunication applications.

The coded mask technics basically work the same way. The signal from the targeted source is mixed through the mask pattern with external signals coming from other sources within the field of view and the background. This creates a shadow on the detection plane that is recorded. Applying deconvolution algorithm to this shadow enables to retrieve the position and intensity of the targeted source.

The choice of the mask pattern

The design of the mask relies on both the sensitivity and the localization accuracy we want to achieve with the instrument. On one hand small size holes will favor the localization accuracy, with a limit on how small they could be being fixed by the size of the pixels of the detection plane. On the other hans, large size holes will increase the instrument sensitivity i.e. increasing the probability for detecting something in the sky. Therefore, the design of the mask is the result of a complex balance between these two parameters. Indeed, the burst position computed by ECLAIRs will be used by the spacecraft to place the burst within the field of view of the MXT and VT telescopes. The mask design shall also ensure that the burst detection efficiency is optimal to fulfill the mission science goals. The optimization of the mask design has been done by computing thousands of mask patterns and by comparing their performances.

Modèle choisi du masque d'ECLAIRs

The selected mask (ACS-o40-46x-a) for the ECLAIRs instrument is made of an array of 46×46 transparent and opaque elements. This mask design is the result of many years of hard work. Credits CEA-APC

Vignetting

The selected mask (ACS-o40-46x-a) for the ECLAIRs instrument is made of an array of 46×46 transparent and opaque elements. This mask design is the result of many years of hard work. Credits CEA-APC

img_instruments08

Left — Only photons within the two blue lines could pass through the mask hole. Right — By removing some materials around the holes, we increase the passage for photons. Credits : Cyril Lachaud, APC

To mitigate the effects of vignetting, the mask thickness shall be less than 0.6 mm. However manufacturing such a thin mask using only a Tantalum sheet (a metal with a good absorbing power for X-ray photons) would have been challenging. In order to increase the mask rigidity, the Tantalum sheet is sandwitched by two Titanium sheets. A silicone joint is placed between the Ta and Ti sheets to absorb vibrations and deformations induced by temperature changes between the two metals. This assembly has been called « TiTaTi » for the Titanium — Tantalum — Titanium sandwitch.

Sandwitch TiTaTi du masque codé d'ECLAIRs

Drawing on the Titanium — Tantalum — Titanium sandwitch used for the ECLAIRs mask. Credits: APC

To mitigate the effects of vignetting, we make sure that the size of the holes in the Titanium sheets are larger than for the Tantalum one.

Maquette du masque

Schematics of the selected ECLAIRs mask. The holes in the Titanium sheets are made larger than for the Tantalum sheet to mitigate the effects of vignetting. Credits: APC

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Published on 02/02/2016
Author : CEA / Irfu
The MXT and the lobster eye

The MXT and the lobster eye

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The MXT and the lobster eye

Biology inspiring astronomy

The truly innovative MXT concentrator developed to study GRBs is a system inspired by biology. Crustaceans of the order of decapods, such as the lobster and crab, have indeed a very particular type of vision. In general,  vision is based on refraction, on the contrary decapods exploit optical reflection. The light is focussed by a number of small channels which cover the eyes of the decapods: a honeycomb structure, although the shape of these channels is not hexagonal but squared. A ray of light can bounce on the wall of the channel being reflected. Eventually, all rays are concentrated in a single central spot.

lobster eye SVOM

Magnification of a crustacean eye. We can distinguish the fine squared cells that completely cover the structure, capturing each ray of light at different angles. Credits: Nasa

 

The advantage of this system is a wide viewing angle. These particular eyes can practically have an open field of view of 180 °. This is helpful for animals living in depth or in turbid environments with little light: they need to collect as much light as possible to identify more quickly predators or food sources in the surrounding environment.

Application to X-rays

En tentant d’y appliquer les principes d’optique, les scientifiques se sont rendu compte que ce type de vision n’est effectif que si la base des canaux est carrée. Phénomène curieux, c’est l’un des rares exemples de forme carrée naturelle en biologie. Idéale en cas de faible lumière, un fort éclairement est au contraire préjudiciable. Plus il y a de rayons, plus ceux-ci vont être réfléchis et causer une image bruitée sur le récepteur. Cette technique prévaut lorsque que le signal/bruit est faible, ce qui est le cas dans la gamme des rayons X. C’est à la fin des années 1970, à Paris, qu’eurent lieu les premières études tentant de réutiliser ce type de vision pour l’observation des rayons X.

Les rayonnements X possèdent la particularité d’être difficiles à réfléchir : la réflexion n’est possible qu’en cas d’incidence rasante. La technique des micro-canaux est donc tout à fait adaptée à ce type de photons car une structure radiale implique que la lumière ne fait qu’un petit angle par rapport à ces surfaces.

Prrincipe MPO

Working principle of a « lobster-eye » optics. Source: http://inspirehep.net/record/1380586/plots

 

To ensure that the point spread function (PSF) is sufficiently small, the size of each single cell of the optics must be very small but still greater than the characteristic wavelength of the light to be reflected. In the case of X-rays, each cell should have a size of the order of few tens of microns. Making an assembly of micro-channels of such size with a metal structure may be hard. However, other materials can be used to manufacture the channels.

MXT imagerie

The point spread function (PSF) describes the spatial distribution of the intensity of light of a point-like source in the focal plane of an optical system. The finer it is, the better the ability to separate two neighboring sources. The image above describes the PSF of the MXT telescope obtained by numerical simulation. The cross results from the optical principle of this telescope based on squared elements.

 

Zoom sur les micro-canaux de verre. La section carrée est parfaitement régulière. Source : inspirehep.net

Zoom on the glass micro-channels. The squared section is perfectly regular. Source: inspirehep.net

 

Micro-channels made of glass

Photonis has put its expertise in processing glass for optical applications to the benefit of the SVOM project. A squared block of glass is heated and then stretched by a weight. Stretching progressively reduces the size of the section. By repeating this process, it becomes possible to obtain regular channels with the desired section size. To obtain the hollow base, it is sufficient to use two types of glass during the process: an external glass and an internal glass with different composition. When a section size of 20 microns is reached, it is sufficient to chemically dissolve the internal glass. The thickness of the external glass is then a few microns. A major difficulty in this process is to avoid twisting the glass during stretching. But the work is not yet done! The micro-channels must then be assembled together. The idea is to assemble different fibers together, in packs of 25, before heating and stretching, to reach the size of 20 microns per fiber. This bundle of fibers is then cut along its width at 90 °. A wafer is thus obtained. The wafer itself is then heated for forming it by means of a press: the surface changes from a flat one to a curved one. Cutting the wafer and shaping it are very complicated phases. Even very small defects can cause degradation of the instrumental response.

To increase the X-ray reflectivity, the leaded glass the micro-channels are made of is immersed in an iridium bath. In all, six months are necessary to produce the 21 wafers corresponding to the complete optics, if no problems arise during the production.

img_instruments02

Schematic of the 21 wafers assembled, consisting each of more than one million glass micro-channels. The different colors represent the different thicknesses of the wafers, from the thinnest (blue) to the thickest (purple). Source: inspirehep.net

 

A great deal of technology

The weight and mass constrains on the SVOM payload suggested the investigation of this type of technology for the observation of X-rays. In fact, the complete optical module developed for SVOM, about 20 cm in diameter, weighs only 1.8 kg. In comparison, the SWIFT SXT instrument developed by NASA weighs several tens of kilos, while the collecting area is only three times larger.

Therefore, this technique seems very promising also for application in future space missions and SVOM, the first one carrying it into orbit, will then represent an interesting case study. Similar optics, but based on silicon pores, are adopted in other projects, such as ATHENA, the future major X-ray observatory developed by ESA to be launched in 2028.

Infos

Published on 02/02/2016
Author : CEA / Irfu & Emanuele Perinati

The ECLAIRs telescope

The ECLAIRs telescope plays a key role onboard SVOM by autonomously detecting Gamma-ray bursts (GRBs) in near real time in the X-/Gamma-ray energy range, and then by quickly providing their position in the sky.

The ECLAIRs consortium is made up of several French labs: IRAP, IRFU & APC. The ECLAIRs telescope is under the CNES supervision.

dessin-ECLAIRs

Figure showing the ECLAIRs telescope. Credit : CEA/CNES

The ECLAIRs instrument is made up of:

  • an X-/Gamma-ray wide-field (89°x89°) coded-mask camera working in the 4 – 250 keV energy range. Each photon passing through the holes in the mask can interact with one (or more) of the 6400 CdTe detectors paving the detection plane called DPIX. The detectors are operated at a temperature of -20°C.
  • a data processing unit called UGTS in charge of operating the telescope, managing the data flow acquisition and searching in near real time for the appearance of new GRBs within the ECLAIRs field-of-view (FoV).

The ECLAIRs wide (2 sr) FoV provides large coverage of the sky. At the top of the instrument there is a coded mask that consists of opaque and transparent elements arranged in a quasi-random pattern. The mask pattern was designed using a mathematical algorithm. The GRB photons can only pass through the transparent elements (i.e. holes). These photons then interact with the DPIX detectors. The resulting image called a shadowgram encloses a partial shadow of the mask. By using deconvolution techniques, it is possible to retrieve the GRB position. The UGTS builds for each detected event a  »photon frame message » including the arrival time, the position on the DPIX and the energy of the event.

Once ECLAIRs triggers on an unknown source (e.g. a GRB), an alert is triggered and immediately sends it to the platform and the ground via the VHF antenna network. If the source is observable by the satellite, the platform will quickly slew to repoint the narrow-field instruments MXT & VT towards the ECLAIRs position in order to search for an X-ray and optical counterpart, respectively.

GRBs are expected to be detected by ECLAIRs with a localisation accuracy better than 10 arcminutes (though as good as 3 arcminutes for very bright GRBs). The ECLAIRs GRB detection rate is expected to be around 70 GRBs per year.

Infos

Author : CEA / Irfu & Olivier Godet

GRM (Gamma Ray burst Monitor)

The gamma ray monitor (GRM) consists of a set of three detectors (GRD Gamma-Ray Detectors) operating in the 15 keV-5 MeV energy range and covering a field of view of 2.6 steradians. These modules are responsible for measuring the spectrum and the variation of the gamma emission during a burst. Each detector consists of a scintillation crystal of sodium iodide (NaI) with a surface of 200 cm2 and a thickness of 1.5 cm attached to a photomultiplier tube. In such device, the incident gamma photon interacts with the scintillator material and the deposited energy is transformed into a bluish light, detected and amplified by the photomultiplier tube.

GRM2

The GRM consists of 3 Gamma-Ray Detectors (GRDs) each inclined by 30° with respect to ECLAIRs pointing axis  – Credit: IHEP

The three identical detectors have a field of view of ± 60 degrees with respect to their axis of symmetry and are inclined by 30 ° with respect to the axis of the ECLAIRs telescope and spaced from each other in the perpendicular plane of 120 °. The three modules, pointing in different directions, have a combined field of view identical to that of ECLAIR. They have a dead time of less than 8 μs, a temporal resolution of less than 20 μs and an energy resolution of 16% at 60 keV.
A calibration detector (GCD) containing a 241 Am radioactive isotope is installed on the edge of each GRD device for gain monitoring and energy calibration. A plastic scintillator placed in front of the NaI crystal (Tl) is used to distinguish low-energy electrons from gamma rays and a charged particle monitor (GPM) helps protect detection modules.

One of the three modules of the Gamma Ray Monitor (GRM). The detector (GRD) is a 200 cm2 Sodium Iodide (NaI) crystal coupled to a calibration detector (GCD) located on the edge. @IHEP

One of the three modules of the Gamma Ray Monitor (GRM). The detector (GRD) is a 200 cm2 Sodium Iodide (NaI) crystal coupled to a calibration detector (GCD) located on the edge. @IHEP

By combining the information of the three detectors, a triangulation can be established and the gamma burst can be located with a precision of 15 ° x15 ° in a wider field of view than that of ECLAIRs. This information may prove invaluable in the search for coincidental events with gravitational wave sources detected by ground-based instruments (LIGO, VIRGO). During a burst of gamma, the GRM can itself trigger an SVOM alert providing the arrival time and the approximate start position to be transferred to the camera ECLAIRs and ground stations (GWAC detectors, gravitational waves, ..).
The GRM should detect a hundred bursts a year.

Institute : IHEP (Beijing, China)

Infos

Published on 2-Nov_2019
Author : bobi

MXT (Microchannel X-ray Telescope)

In response to alerts transmitted by the ECLAIRs, the Microchannel X-ray Telescope (MXT) will observe gamme ray bursts (GRBs) in the soft X-ray range (energy between 0.2 and 10 KeV), from the very beginning of their afterglow emission. The MXT is being developed in France by CNES and CEA/Irfu, in close collaboration with the University of Leicester in the United Kingdom and the Max-Planck Institute für extraterrestische Physik in Germany.

Instrument MXT

Sketch of the MXT: the diameter of the optics is 24 cm, the focal length is 1.15 m and the tube is made of carbon fiber. The optical module has a weight of 1.8 kg while the entire assembly (optics, tube, radiator, camera and on-board computer) weighs 35 kg. Credit: CEA / CNES

The MXT is composed by an optical module based on 40 mm sized micro-channel plates, making a so-called micro-pore optics (MPO), coupled to a focal plane camera equipped with an X-ray sensitive pnCCD.  The MXT will deliver images and spectra of sources in the 0.2-10 keV range with an energy resolution as good as ~75 eV (at 1.5 keV). The field of view of the instrument is 1.1° x 1.1°.

The MXT is conceived to locate sources much more precisely than the ECLAIRs does, with an accuracy of less than 1 arcmin, which increases up to ~20 arcsec in the case of very bright sources. This second step in the localization process will then permit, using also images obtained by the visible telescope VT, to refine the position of the observed sources. The position will be automatically calculated on board and transmitted to the ground via the VHF alert network.

With a detection sensitivity of ~10-12 erg/cm2/sec reachable in a ~10 kse (10 000 s) long observation, the MXT will be able to follow the evolution of the afterglow emission for a whole day after the initial prompt signal.

This sensitivity will enable the determination of the spectral index, which is the form of the energy distribution of the emission. This parameter is important because it permits to reconstruct the distribution of energetic particles responsible for the X-ray emission as well as obtain information on the physics of the shocks. Moreover, thanks to its soft operational band the MXT will allow to measure the absorption on the line of sight of the emission originating from the GRBs, which occurs both in the intergalactic medium and in the host galaxies.

Infos

Author : CEA / Irfu & Emanuele Perinati

The Visible Telescope (VT)

The VT telescope (Visible Telescope) is a dedicated optical tracking telescope, onboard the SVOM satellite. Its main purpose is to detect and observe the emission in visible light, produced immediately after a gamma burst. In less than 10 minutes after the alert given by the ECLAIRS camera and using the refined position provided by the MXT instrument, this instrument is able to reconstruct the position of the gamma burst with an accuracy of a few seconds of arc. The VT is expected to detect and locate about 60 gamma bursts per year.

VT

The VT is composed by a mirror 40 cm in diameter. The focal plane includes two CCD cameras, one red channel and one blue channel. Credit: NAOC

The VT telescope is a Ritchey-Christian telescope with a 40 cm primary mirror and a field of view of 26 arc minutes x 26 arc minutes. Its focal plane is equipped with two 2048 × 2048 CCD cameras covering two wavelength ranges: the blue channel from 450 to 650 nm and the red channel from 650 to 1000 nm. The blue channel CCD is a thinned, backlit detector, while the red channel CCD is specially processed to achieve high sensitivity at long wavelengths. The quantum efficiency of the red channel CCD is greater than 50% at 0.9 μm, allowing the VT telescope to reach the visual magnitude of 22.5 in 300 seconds. The VT is expected to detect very far-distant gamma-ray bursts with a redshift greater than 6.5, corresponding to distances more than 12 billion years away.

Optical paths (left) and spectral responses (right) of the two red and blue channels of the VT telescope. @NAOC

Optical paths (left) and spectral responses (right) of the two red and blue channels of the VT telescope. @NAOC

In order to quickly provide the position of gamma ray bursts with a precision less than the arc second, the VT telescope carries out on-board data processing. After the localization of a gamma burst by the MXT instrument co-aligned with the VT telescope, lists of possible sources are extracted from the successive images obtained by the VT telescope, centered on the gamma burst position provided by the MXT.
These lists are transmitted in near real time via the VHF high-frequency network, to allow the ground-based software to produce finding charts  and to search for the optical equivalent of the gamma-ray burst, by comparing to existing catalogs. If a counterpart is identified, an alert is broadcast to the world astronomical community to trigger observations using large ground-based telescopes, in particular to measure the redshift of the gamma-ray burst.

VT telescope test model and test facility at Xinglong Observatory (Beijing, China). @NAOC

VT telescope test model and test facility at Xinglong Observatory (Beijing, China). @NAOC

According to the results of the Swift mission, confirmed high red-shift gamma-ray bursts are rare, contrary to theoretical calculations that predict a fraction greater than 5 to 7%. This is probably because, for most of the gamma-ray bursts detected by Swift, optical tracking images are not deep enough to allow for rapid identification, preventing large ground-based telescopes from performing spectroscopic observations.
The SVOM mission will greatly improve this situation thanks to the high sensitivity of the VT telescope, especially for long wavelengths, and the generation of quick alerts on the visible counterpart of the burst. In addition, the SVOM pointing strategy, in the opposite direction to the sun, allows gamma ray bursts to be observed very early using large ground-based spectroscopic telescopes. As a result, it is expected that more high redshift gamma ray bursts will be identified by SVOM.

Institutes: NAOC Beijing, XIOPM Xian (China)

Infos

Published on 2-Nov-2019
Author : bobi

The alert network

The alert network based on a French design is one of the key features of the SVOM mission enabling the near real time dissemination of information between the satellite and the ground. It plays a crucial role in the optimization of the synergy for the GRB multiwavelength follow-up. This effort is needed to ensure that the distance to the GRB can be measured.

Given the rather short duration of GRBs, the alert network is designed to dispatch, as soon as possible, all science data needed for ground telescopes to rapidly follow-up of the GRBs detected by ECLAIRs. Once a GRB is detected onboard, the alert message is transmitted to the ground in about 10 seconds at very high frequency (VHF) in a frequency band between 137 and 138 MHz by an onboard antenna. The message is then downlinked through a network of radio stations spread around the Earth’s equator.

Map showing the locations of the VHF antenna network as of September 24, 2020, in green the deployed stations, in grey the upcoming stations – Credit: CNES

Map showing the locations of the VHF antenna network as of September 24, 2020, in green the deployed stations, in grey the upcoming stations – Credit: CNES

At least 43 VHF antennae will be homogeneously deployed in the inter-tropical zone around the Earth, between latitudes -30° and +30°. They will relay every alert message from the satellite to the French Science Center (FSC) located at Saclay in France.

The VHF messages will summarize the main GRB properties that are needed for the follow-up. After a first analysis at the FSC, the messages will be distributed to the whole scientific community, in particular to the GFTs robotic telescopes that will refine the GRB position and give an initial indication of distance. A summary of the GFT results will then be sent back to the FSC in order to share their findings with large observing facilities.
The performance objective of this network is to enable the alert message to be transmitted to the robotic telescopes in less than 30 seconds after detection on board the satellite. The results of the observations from the GFT telescopes are sent back to the FSC and finally disseminated to the large telescopes. These large telescopes, with a smaller field of view, will allow the acquisition of the spectrum of the burst and thus the estimation, by measuring the redshift, of its distance. If everything goes smoothly, it should take less than 4 min to start acquiring GRB optical spectra with large telescopes.

As of October 02, 2020 the deployed network is composed of 16 stations.

Chronology of station installation

Infos

Author : CEA / Irfu & CNES

GWAC (Ground-based Wide Angle Camera)

The main science objective of the Ground-based Wide Angle Camera (GWAC) is to observe in the visible range (between 500 and 850 nm) from the ground, the prompt emission of some of the gamma-ray bursts detected by the camera ECLAIRs.
The instrument consists of 10 mountings, each carrying 4 cameras 18 cm in diameter, covering a field of view of about 5000 degrees2, roughly half of the field of view of the ECLAIRs telescope.
Each of the 40 cameras is equipped with a 4096 × 4096 E2V CCD operating in the 0.5 to 0.85 μm wavelength band with a field of view (FoV) of 150 deg². GWAC provides source locations up to a visible magnitude mv = 16 with an accuracy of 11 arcsec (for a 10 s exposure).

Panoramic view of GWAC installation at Xinglong Observatory (Beijing, China) showing 4 GWAC mountings (right) and 60cm and 30cm telescopes (left). @NAOC

Panoramic view of GWAC installation at Xinglong Observatory (Beijing, China) showing 4 GWAC mountings (right) and 60cm and 30cm telescopes (left). @NAOC

GWAC searches in real time for visible counterparts around the coordinates of bursts provided by the other instruments (ECLAIR, GRM, MXT, VT, TFG and others). In addition to the VT telescope aboard SVOM, GWAC provides a wide field coverage of the sky regions observed by SVOM.
GWAC also has the ability to detect optical transient events itself without external triggers. Two 60 cm telescopes and 30 cm telescopes are installed next to GWAC to confirm transient detections and to verify whether they are real or false events, providing coordinates with an accuracy of 1 arcsec.

GWAC module of 4 cameras and 60 cm telescopes at Xinglong Observatory. @NAOC

GWAC module of 4 cameras and 60 cm telescopes at Xinglong Observatory. @NAOC

It is foreseen that GWAC will be divided into two sub-sets, each of them consisting of 20 cameras and a 60cm diameter  follow-up telescope. One set will be installed at CTIO in Chili and the other part at the ALI observatory in the west of Tibet.
GWAC is designed to observe more than 12% of SVOM gamma-ray bursts in the visible band from 5 minutes prior to 15 minutes after initiation.

Infos

Published on 2-Nov-2019
Author : bobi

GFT (Ground Follow-up Telescope)

GFT (Ground Follow-up Telescope) robotic telescopes are essential for observing and studying gamma-ray bursts. Particularly responsive, they point to the localization area communicated by the satellite through the VHF alert network, in less than a minute. These tracking telescopes will provide an accurate measure (of the order of the arc second) of the celestial coordinates of the burst, as well as the photometric evolution of the emission in several spectral bands (from the visible range to the infrared). They will also provide an estimate of its distance (by the redshift measure).
The results are then sent to the French Science Center (FSC), which will relay the alert message to larger telescopes, such as the New Technology Telescope (NTT) and the Very Large Telescope (VLT) for visible light optics. or ALMA observatory for radio waves.
The SVOM mission will implement two robotic telescopes with a primary mirror at least 1m in diameter. One will be based in San Pedro Martir in Mexico under French responsibility, the other at the Jiling Observatory under Chinese responsibility.

F-GFT Ground tracking telescope (France)

Site de SanPedro Martir

Left – View of the San Pedro Martir site in Mexico where the French GFT will be installed. Right – Image showing what the French GFT will look like.

C-GFT Ground Tracking Telescope (China)

The Chinese Ground Tracking Telescope (C-GFT) is based on an existing 1 m telescope located at the Jiling Observatory in China, which is a f / 8 Ritchey-Christian system, allowing rapid repointing through a altazimutal mount. It will be upgraded with a dichroic mirror system, 3 SDSS filter channels (g, r and i), a robotic control system and a real-time data and communication system.

The dome and Chinese ground-based telescope (C-GFT), 1 m in diameter, at the Jilin Observatory (Jilin, China).

The dome and Chinese ground-based telescope (C-GFT), 1 m in diameter, at the Jilin Observatory (Jilin, China).

The three channels will be equipped with low read time CMOS-CCD cameras of size 2K × 2K, corresponding to a FoV of 21 × 21 arcmin2, operating in the 0.4 to 0.95 μm band. The sensitivity of C-GFT will reach mag (r) = 19 (at 5σ, AB mag) for 100 s of exposure time during the nights of the new moon.
In addition to Jiling’s dedicated C-GFT observatory, another  1 m telescope will be installed by the NAOC (National Astronomical Observatory of China) at Ali Observatory, Tibet, in western China. The NAOC will have access to approximately 2,500 observation hours per year, which could be dedicated to SVOM gamma-ray burst monitoring via alerts with a typical response time of approximately 15 min.

Infos

Published on 2-Nov-2019
Author : bobi

FSC (French Science Center)

The French Science Center will analyze the VHF alert data in an automated fashion in near real time in order to distribute the information needed to follow-up the burst with large observing facilities. The alert data will be also analyzed by Burst Advocates, French and Chinese scientists on duty H24, who will enrich the science data content.

Screenshot 2016-02-21 at 09.42.04

Functional diagram of the French ground segment showing the interfaces between the various French entities (FSC, FPOC and the instrument centers) as well as the interfaces with the entities of the Chinese ground segment.

During the whole observing sequence of a GRB, the recorded data will be reduced in real time to generate scientific products (e.g. the GRB duration, the peak energy Epeak, lightcurves in different energy bands, etc…), that will be made available to the scientific community through a dedicated web interface.

The French and Chinese ground segments manage both the operations and calibration of their instruments as well as the archiving of all science data.

Infos

Author : CEA / Irfu & Olivier Godet
MASPALOMAS – ESP2 station (Canary islands)

MASPALOMAS – ESP2 station (Canary islands)

MASPALOMAS – ESP2 station (Canary islands)

MANILLE Image 1

Location of Maspalomas station, in Canary islands – global view

          Name : ESP2

          Location : MASPALOMAS on the island of GRAN CANARIA

          Latitude : 27.72

          Longitude: -15.63

          Hosting : INTA site (Instituto Nacional de Tecnica Aeroespacial)

          Start-up : September, 25 2020

Location of the Maspalomas station on Gran Canaria Island

Location of the Maspalomas station on Gran Canaria Island

Location of the Maspalomas station on Gran Canaria Island, close-up view

Location of the Maspalomas station on Gran Canaria Island, close-up view

This station was installed on the roof of a building on the INTA (Instituto Nacional de Tecnica Aeroespacial) site.
A concrete slab was placed on the roof to house the station.

Maspalomas3

Installation of the SVOM antenna on the INTA site

Installation of the SVOM antenna on the INTA site

This station can be configured to receive data from the NOAA 18 and NOAA 19 weather satellites. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

Image construted from the data sent by the NOAA18 satellite

Image construted from the data sent by the NOAA18 satellite

 

Infos

Author : CEA-Irfu & CNES
WISE (Israel) – ISR1 station

WISE (Israel) – ISR1 station

WISE (Israel) – ISR1 station

MANILLE Image 1

Location of Wise station in Israel – global view

          Name : ISR1

          Location : Negev desert

          Latitude : 30.59

          Longitude: 34.76

          Hosting : Wise Astronomical Observatory

          Start-up : September, 10 2020

Location of Wise station - close-up view[

Location of Wise station – close-up view[

Location of Wise station - close-up view[

Location of Wise station – close-up view[

This station has been deployed on the Wise Observatory site. The observatory is located 200km south of Tel Aviv, in the Negev desert, near the city of Mitzpe Ramon. The SVOM station is installed on the southernmost part of the site.

Global view of the Wise observatory

Global view of the Wise observatory

The local team that installed the station[

The local team that installed the station[

This station can be configured to receive data from the NOAA 18 and NOAA 19 weather satellites. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

Image construted from the data sent by the NOAA18 satellite

Image construted from the data sent by the NOAA18 satellite

 

Infos

Author : CEA-Irfu & CNES
CAPE VERDE – CPV2 station

CAPE VERDE – CPV2 station

CAPE VERDE – CPV2 station

MANILLE Image 1

Location of Cape Verde station – global view

          Name : CPV2

          Location : Cape Verde

          Latitude : 14.92

          Longitude: -23.51

          Hosting : on the site of the NOSI (DATA CENTER) in Praia

          Start-up : August, 31 2020

Location of Cape Verde station - close-up view

Location of Cape Verde station – close-up view

Location of Cape Verde station - close-up view

Location of Cape Verde station – close-up view

This station was deployed on the roof of the NOSI Data Center building in Praia on Santiago Island.

The station was installed on the roof of the  DATA Center

The station was installed on the roof of the DATA Center

This station can be configured to receive data from the NOAA 18 and NOAA 19 weather satellites. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

Image construted from the data sent by the NOAA18 satellite

Image construted from the data sent by the NOAA18 satellite

 

Infos

Author : CEA-Irfu & CNES
ASCENSION – SHN1 station

ASCENSION – SHN1 station

ASCENSION – SHN1 station

MANILLE Image 1

Location of Ascension island station – global view

          Name : SHN1

          Location : Ascension Island

          Latitude : -7.92

          Longitude: -14.33

          Hosting : ESA Ariane site

          Start-up : August, 24 2020

Location of Ascension island station - close-up view

Location of Ascension island station – close-up view

Location of Ascension island station - close-up view

Location of Ascension island station – close-up view

This station was installed on the ESA’s Ariane site, where the CNES launcher tracking station is located.The Ariane site is located on the east coast of the island. This site already hosts the REGINA and DORIS stations. The station is attached to the building that houses the Ariane site’s generator set.

Global view of the site

Global view of the site

The station is attached to the wall of the building housing the generators

The station is attached to the wall of the building housing the generators

This station can be configured to receive data from the NOAA 18 and NOAA 19 weather satellites. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

Image construted from the data sent by the NOAA18 satellite

Image construted from the data sent by the NOAA18 satellite

 

Infos

Author : CEA-Irfu & CNES
HO CHI MINH – VNM2 station

HO CHI MINH – VNM2 station

HO CHI MINH – VNM2 station

MANILLE Image 1

Location of Ho Chi Minh station – global view

          Name : VNM2

          Location : periphery of Ho Chi Minh City

          Latitude : 11.83

          Longitude: 106.85

          Hosting : Vietnamese-German University at Binh Duong

          Start-up : August, 24 2020

Location of Ho Chi Minh station - close-up view

Location of Ho Chi Minh station – close-up view

Location of Djibouti station - close-up view[

Location of Djibouti station – close-up view

This station was deployed on a building on the campus of the Vietnamese-German University in Binh Duong, on the outskirts of Ho Chi Minh City, Vietnam.

Station deployed on the roof of the university in Binh Duong

Station deployed on the roof of the university in Binh Duong

This station can be configured to receive data from the NOAA 18 and NOAA 19 weather satellites. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

Image construted from the data sent by the NOAA18 satellite

Image construted from the data sent by the NOAA18 satellite


 

Infos

Author : CEA-Irfu & CNES
DJIBOUTI – DJ1 station

DJIBOUTI – DJ1 station

DJIBOUTI – DJ1 station

MANILLE Image 1

Location of Djibouti station – global view

          Name : DJ1

          Location : Djibouti

          Latitude : 11.53

          Longitude: 42.86

          Hosting : on the site of the Arta observatory

          Start-up : March, 04 2020

Location of Djibouti station - close-up view

Location of Djibouti station – close-up view

Location of Manila station - close-up view

Location of Manila station – close-up view

This station was deployed on the site of the observatory of Arta located in the city of the same name in the Republic of Djibouti.

The staion as been installed

The station has been installed on the roof of the observatory

The station was installed on the roof of the observatory.

The local team that installed the station

This station can be configured to receive data from the NOAA 18 and NOAA 19 weather satellites. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

Image contruted from the data of the NOAA18 satellite

Image construted from the data sent by the NOAA18 satellite

 

Infos

Author : CEA-Irfu & CNES
MANILA-PHL1 station

MANILA-PHL1 station

MANILA-PHL1 station

MANILLE Image 1

Location of Manila station – global view

          Name : PHL1

          Location : Manila – Philippines

          Latitude : 14.53

          Longitude: 121.04

          Hosting :National Mapping and Resource Information Authority

          Start-up : January, 22 2020

MANILLE Image 2

Location of Manila station – close-up view

The Manilia staion, close-up view

Location of Manila station – close-up view

This station was deployed on the roof of the NAMRIA (National Mapping and Resource Information Authority) building in the city of Manila.

Sation installed at the top of the NAMRIA building at Manila

Sation installed at the top of the NAMRIA building at Manilia

This station can be configured to receive data from the NOAA 18 and NOAA 19 weather satellites. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

Image constructed from data sent by the NOAA18 satellite.

Image constructed from data sent by the NOAA18 satellite.

REUNION-REU1 station

REUNION-REU1 station

REUNION-REU1 station

LA REUNION Image 1

Location of the Reunion Island station – global view

          Name : REU1

          Location : La Réunion – océan Indien

          Latitude : -21.2

          Longitude: 55.57

          Hosting : Volcanological Observatory of Piton de la Fournaise

          Start-up : January, 22 2020

LA REUNION Image 2

Location of the Reunion Island station – close-up view

The Reunion station is located on a building of the observatory of Piton de la Fournaise, one of the most active volcanoes on the planet, culminating at 2632m. Covering an area of 2,512 km2, this island is located in the Mascarene archipelago 172 km west-southwest of Mauritius and 679 km east-southeast of Madagascar.

LA REUNION Image 3

Location of the Reunion Island station – close-up view

LA REUNION Image 4

Station installed in Reunion Island

Currently this station is configured to receive data from the NOAA 19 weather satellite. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

LA REUNION Image 5

Image reconstructed in infrared from data sent by the NOAA 19 satellite

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AMSTERDAM-ATF1 station

AMSTERDAM-ATF1 station

AMSTERDAM-ATF1 station

AMSTERDAM Image 1

Location of the Amsterdam station – global view

          Name : ATF1

          Location : Amsterdam Island – Indian Ocean

          Latitude : -37.79

          Longitude: 77.57

          Hosting : GEOPHY Building

          Start-up : January, 17 2020

AMSTERDAM 2

Location of the Amsterdam station – close-up view

Amsterdam Island is a French island located in the central Indian Ocean, 1368 km north-northeast of the Kerguelen Islands and 2713 km southeast of Mauritius. Together with the island of Saint-Paul, 91 km further south, it forms the district of Saint-Paul and New Amsterdam, one of the five districts of the French Southern and Antarctic Lands. It is the least accessible station in the network: about 20 people live on the island of Amsterdam during the southern winter and 40 in the summer.

AMSTERDAM Image 2

Location of the Amsterdam station – close-up view

AMSTERDAM Image 3

Station installed in Amsterdam

Currently this station is configured to receive data from the NOAA 19 weather satellite. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

AMSTERDAM Image 4

Image reconstructed in infrared from data sent by the NOAA 19 satellite

SONGKHLA-THA2 station

SONGKHLA-THA2 station

SONGKHLA-THA2 station

THAILANDE Image 1

Location of Songkhla station – global view

         Name : THA2

         Location : Songkhla – Thailand

         Latitude : 7.16

         Longitude : 100.61

         Hosting : Regional Observatory for the Public

         Start-up : January, 15 2020

THAILANDE Image 2

Location of Songkhla station – close-up view

Songkhla is a city in the southern region of Thailand, capital of Songkhla province. It is one of the most important ports in the east of the Malay Peninsula. The station is installed on the site of the Regional Observatory for the Public (Regional Astronomical Observatory for the Public) which is owned by the National Astronomical Research Institute of Thailand (NARIT).

THAILANDE Image2

Location of Songkhla station – close-up view

THAILANDE Image 3

Station installed in Songkhla

Currently this station is configured to receive data from the NOAA 19 weather satellite. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

SAINT-HELENA-SHN2 station

SAINT-HELENA-SHN2 station

SAINT-HELENA-SHN2 station

Image1 Sainte-Helene

Location of the St. Helena station – global view

          Name : SHN2

          Location : Saint Helena – Atlantic Ocean

          Latitude : -15.9425

          Longitude: -5.6672

          Hosting : St Helena Met Office

          Start-up : November, 12 2019

Image 2 Sainte-Helene

Location of the St. Helena station – close-up view

The St. Helena station is located on the east side of the island, near the town of Longwood. The island of St. Helena is a 122 km² British island with a population of less than 5,000. It is located 1856 km from the African coast and 3286 km from the South American coast.

SAINTE-HELENE Image 2

Location of the St. Helena station – close-up view

SAINTE-HELENE Image 3

Station installed in Saint Helena

Currently this station is configured to receive data from the NOAA 19 weather satellite. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

SAINTE-HELENE Image 4

Image reconstituted in infrared from data sent by the NOAA 19 satellite

LIBREVILLE-GAB1 station

LIBREVILLE-GAB1 station

LIBREVILLE-GAB1 station

Image1 Libreville

Location of the Libreville station – global view

          Name : GAB1

          Location : Libreville – Gabon

          Latitude : 0.3554

          Longitude: 9.4496

          Hosting : Ariane Downstream Telemetry Station

          Start-up : August, 22 2019

Image 2 Libreville

Location of the Libreville station – close-up view

Libreville station is located in N’Koltang, Gabon, 40 km from Libreville airport. It is installed on a site that is part of an ESA network of downlink telemetry stations, used in particular to monitor the Ariane, Vega and Soyuz launchers.

LIBREVILLE Image 2

Location of the Libreville station – close-up view

LIBREVILLE Image 3

Station installed in Libreville

Currently this station is configured to receive data from the NOAA 19 weather satellite. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

LIBREVILLE Image 4

Image reconstituted in infrared from data sent by the NOAA 19 satellite

SANTA-MARIA-PRT1 station

SANTA-MARIA-PRT1 station

SANTA-MARIA-PRT1 station

Image1 Açores

Location of Santa-Maria station – global view

          Name : PRT1

          Location : Santa-Maria – Azores

          Latitude : 36.9858

          Longitude: -25.1262

          Hosting : Site of Estação Geodésica Fundamental RAEGE

          Start-up : July, 24 2019

Image 2 Açores

Location of Santa-Maria station – close-up view

The Santa-Maria station is located on the roof of the RAEGE (Red Atlantica de Estaciones Geodinamicas y Espaciales) station in the center of the island north of the airport. This 97 km² island is part of the Portuguese archipelago of the Azores. It is inhabited by about 5500 people and is located 1450 km west of Lisbon.

ACORES Image 2

Location of Santa-Maria station – close-up view

ACORES Image 3

Station installed in Santa-Maria

Currently this station is configured to receive data from the NOAA 19 weather satellite. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

ACORES Image 4

Image reconstituted in infrared from data sent by the NOAA 19 satellite

ATHENS-GRC1 station

ATHENS-GRC1 station

ATHENS-GRC1 station

Image1 AThenes

Location of Athens station – global view

          Name : GRC1

          Location : Athens – Greece

          Latitude : 37.9751

          Longitude: 23.7799

          Hosting : Roof of the National Technical University of Athens

          Start-up : June, 24 2019

The Athens station is located in the city centre, more precisely in the Zográfou district. It is relatively close (4 km) to a field of FM transmitting antennas that can generate interference.

Image 2 Athènes

Location of Athens station – close-up view

ATHENES Image 2

Location of Athens station – close-up view

ATHENES Image 3

Station installed in Athens

Currently this station is configured to receive data from the NOAA 19 weather satellite. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

ATHENES Image 4

Image reconstituted in infrared from data sent by the NOAA 19 satellite

KOUROU-GUF1 station

KOUROU-GUF1 station

KOUROU-GUF1 station

Image1 Kourou

Location of Kourou station – global view

          Name : GUF1

          Location : Kourou – French Guiana

          Latitude : 5.1714

          Longitude: -52.68

          Hosting : Mercure building on the Guiana Space Center (CSG)

          Start-up : May,16 2019

Image 2 Kourou

Location of Kourou station – close-up view

The Kourou station is located on the CSG Technical Centre. This centre, jointly managed by CNES, which is the owner, ESA and Arianespace, is located 80 km from Cayenne airport.

KOUROU Image 2

Location of Kourou station – close-up view

KOUROU Image 3

Station installed in Kourou

Currently this station is configured to receive data from the NOAA 19 weather satellite. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

KOUROU Image 4

Image reconstituted in infrared from data sent by the NOAA 19 satellite

HBK-ZAF1 station

HBK-ZAF1 station

HBK-ZAF1 station

Image1 HBK

Location of the HBK station – global view

          Name : ZAF1

          Location : Hartebeesthoek (HBK) – South Africa

          Latitude : -25.8872

          Longitude: 27.7075

          Hosting : Site of SANSA (South African National Space Agency)

          Start-up : April 26, 2019

Image 2 HBK

Location of the HBK station – close-up view

The HBK station is located on the SANSA site in South Africa, 100 km from Johannesburg airport.

HBK Image 2

Location of the HBK station

HBK Image 3

Station installed at HBK

Currently this station is configured to receive data from the NOAA 19 weather satellite. The reconstructed images make it possible to check the quality of the site and to identify possible degradations on the reception of the signals.

HBK Image 4

Image reconstituted in infrared from data sent by the NOAA 19 satellite

VHF stations

VHF stations

VHF stations

The design

The stations installed on each site are supplied by CNES and manufactured by INGESPACE. They all have the same architecture, i.e. a mast on which is placed a platform supporting two antennas circularly polarized in opposite directions.

Station 1

Mast and antennas – 3D representation and reality Credits: CNES

The set rests on a foot allowing to integrate the station where one wishes. There are several designs of the antenna stand to adapt to the constraints of the host site.

A waterproof housing is placed in the upper part of the station mast. In this box are the electronics for processing the signal received by the antennas and the modem for data transmission to the French Scientific Centre (FSC) via the Internet.

Station 2

Location of the electronic box – example of the Santa Maria station – Credits: CNES

The installation

Each station is installed to have as few caches as possible so that the signals received by the antennas are not disturbed. A survey around the antenna is therefore carried out at the time of installation to identify the masks.

To communicate with the station and transmit data to the FSC only an internet connection is required. In most cases an Ethernet cable is used to connect the antenna to an Internet access switch. But for some very isolated sites a 4G mobile link will be installed.

Thereafter, the station operates in a totally passive way by receiving the data frames sent, today by the NOAA (National Oceanic and Atmospheric Administration) satellites and from 2022 by the SVOM satellite.

Test phase with NOAA satellites

Pending the launch of the SVOM satellite, the stations are configured to receive signals from either the NOAA 18 or NOAA 19 satellites. These NOAA (National Oceanic and Atmospheric Administration) satellites are US weather satellites launched in 2005 and 2009 respectively. They are in polar orbit around the Earth at an altitude of 850 km and have a period of 101-102 minutes. Their initial objective is to observe meteorological phenomena, particularly in the marine environment.

For the SVOM mission, these satellites are used to test the quality of reception facilities. In fact, these satellites pass over the station several times a day and send data that enable an image of the Earth and the atmosphere to be reconstructed.

These data are sent in APT (Automatic Picture Transmission) mode at frequencies of 137.9125 MHz for NOAA 18 and 137.100 MHz for NOAA 19. Two categories of images are formed: infra-red and visible in order to have a readable image for any passage of day or night.

Station 3

Visible image received by a station in Saclay Credits: CEA

Station 4

Infrared image received by a station in Saclay Credits: CEA

The NOAA satellites

The NOAA satellites

The NOAA satellites

Presentation

The NOAA (National Oceanic and Atmospheric Administration) satellites are American meteorological satellites in polar orbit at an altitude of around 850 km. They belong to the observation system set up by the World Meteorological Organization. The first NOAA satellite was launched in 1970 and since then 20 NOAA satellites have been put into orbit. Currently, the NOAA 15, NOAA 18, NOAA 19 and NOAA 20 satellites are in service. The first three are from the fifth generation of these satellites, the NOAA POES (Polar Operational Environmental Satellites), and are gradually being replaced by satellites such as Suomi NPP launched in 2011 and by JPPS (Joint Polar Satellite System) satellites, of which NOAA 20 is a part. The next three JPPS satellites are scheduled for launch in 2022 and 2031.

NOAA 1

Artist view NOAA 18

These satellites are dedicated to meteorological observations, in particular the observation of phenomena impacting the marine environment. For these studies, various instruments are embarked, including a radiometer to monitor cloud masses in order to measure maritime or continental surface temperatures, an infrared sounder providing temperature and humidity profiles of the atmosphere and a scatterometer to determine the direction and speed of winds over maritime surfaces.

Characteristics of the NOAA 18 and NOAA 19 satellites

NOAA 2
Their period of revolution is such that each satellite flies over the equator 14 times a day, in ascending and descending passages. The same region is overflown at least 4 times a day by the same satellite at an interval of about 6 hours.

Interest in the SVOM mission

SVOM is scheduled to be launched at the end of 2021. These satellites will be used to test upstream the reception of signals by the antennas of the alert network, which is currently being deployed. The APT frequency of these satellites is close to the SVOM alert transmission frequency (137-138 MHz), which makes them very interesting satellites for this test phase. The images reconstructed by the stations from the signals sent by NOAA 18 and NOAA 19 make it possible to estimate the quality of the installation site and to predict possible disturbances that could have an impact on the reception quality of the signals sent by SVOM.

The APT mode

APT (Automatic Picture Transmission) mode is an analog picture transmission system. Observation satellites are equipped with a scanning radiometer, a system consisting of several lenses, sensors and mirrors controlled by motors. The radiometer scans the Earth’s surface line by line and as the satellite moves, a complete image is built up using an imager. 120 lines are transmitted every minute. The name APT comes from the fact that the transmission of these images is automatic and continuous.

Type of image reconstructed

Each image is constructed in the same way. From left to right we can see: a synchronization band, a time marker, the image itself and a telemetry band. This succession is repeated twice, with the visible image on the left and the infrared image on the right.

NOAA 3

Format of the frames transmitted in APT mode

At each frame reception, the synchronization appears as vertical black lines on the left side of the image while the telemetry data appears as « wedges » carrying calibration and other information. The markers are alternating horizontal black and white traces for the visible channel, white and black traces for the infrared channel, the synchronization is alternating vertical bands and the telemetry is alternating grey level bands used as a reference to decode the image.
Here is the type of images reconstructed by the stations after receiving the signal from a NOAA satellite:

NOAA 4

Example of images reconstructed by the test station in Toulouse: the image on the left is made in infrared and the one on the right in visible light

For the test phases through the study of these images, only infrared images are considered because they can be made at any time and their quality is less random than those made in the optical field.

Videos

Videos

3D-print your coded mask

3D-print your coded mask

3D-print your coded mask

If technology had allowed it, the coded mask of the ECLAIRs instrument might have been made in 3D printing. But what was not possible for the real flight model is possible for a model. So here are the STL files allowing to manufacture a replica of the coded mask in ¼ scale.

The STL files have been adapted from the CAD (computer aided design) of the original model to allow a scale ¼ printing in good conditions : The plate thicknesses were slightly increased to accommodate the capabilities of the printers and some small parts were either merged with the main parts or simply removed.

Parts composing the mask and correspondence with the different files to download.

Parts composing the mask and correspondence with the different files to download.

In practice, the 4 files correspond to the 4 parts shown in the figure. As the real mask is made partly of titanium, partly of tantalum, it can be of the most beautiful effect to print the tantalum part in one color (ECLAIRs_Coded_Mask_FM1_Tantalum) and the rest in another. Don’t hesitate to send pictures of your realizations!!

Many thanks to the APC laboratory team for supplying the CAD model and to Aubin Guillemot for his work in adapting the STL files.

Let’s play with ECLAIRs

Let’s play with ECLAIRs

Let’s play with ECLAIRs

The IMASCOD simulator (for CODed MASk Imaging) is a simplified way to illustrate the ECLAIRs coded-aperture telescope imaging process. This simulator was programmed in Python language, originally as a demonstrator for school and CEA open days.

This simulator makes it possible to build the image recorded by the detector. Once the image is created, an algorithm based on the same principle as that applied in the system of gamma-ray bursts trigger (Scientific Processing Unit) on board ECLAIRs is used.

Instructions:

To begin, choose the position of a point source in the sky (a burst gamma for example) that will be detected by ECLAIRs. This position is expressed in cartesian coordinates (x, y) in the field of view of the telescope, where the position x = 0, y = 0 corresponds to the lower left corner. The size of the sky image is 200 × 200 (x and y should not exceed 199).

Once the position is defined, the photons of the source are propagated through the instrument. In the same way, photons of the diffuse background noise of the sky are added.

When you have updated the input parameters, click on « Run »! The results will first display the image of the detector plane recorded by ECLAIRs, then the image of the reconstructed sky.

Parameters:

x

y

Number of photons of the source

Number of photons of the background noise