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

If the heart of the SVOM mission is to guarantee the observation of approximately one hundred gamma-ray bursts per year, it is above all a formidable tool designed to scrutinize the transient sky as a whole.

Transient phenomena

Various astronomical objects are called « transient » because they change over time. These changes are distinguished in particular by a variation in their luminosity or their observed position and can be caused by movement or by transformation of the source itself. The time scales of transient phenomena are diverse,  from seconds, to hours or days, and require appropriate observational strategies. Gamma-ray bursts are among the most studied transient phenomena, but there are many others, such as supernovae, eruptive stars (mostly red dwarfs and potentially some brown dwarfs) or active galactic nuclei.

Artist's view of a very violent eruption on one of the red dwarfs of the couple of DG Canum Venaticorum or DG CVn, located about 60 light years from the Solar System. On April 23, 2014, the Swift satellite's BAT (Burst Alert Telescope) instrument gave the alert for a thorough observing campaign. Credit: NASA, Goddard Space Flight Center, S. Wiessinger

Artist’s view of a very violent eruption on one of the red dwarfs of the couple of DG Canum Venaticorum or DG CVn, located about 60 light years from the Solar System. On April 23, 2014, the Swift satellite’s BAT (Burst Alert Telescope) instrument gave the alert for a thorough observing campaign. Credit: NASA, Goddard Space Flight Center, S. Wiessinger

This field of ​​research is rapidly expanding and it could yield potential discoveries on the physics associated with violent cosmic phenomena . However, this requires significant detections and monitoring devices. SVOM is able to meet these expectations.

Like its sister mission SWIFT developed by NASA, SVOM includes in its program significant room for non-gamma-ray burst related science. The field of gamma-ray observation is rich in transient events. Sweeping the sky with its multi-wavelength instruments, SVOM can issue an alert following the detection of transient phenomena, communicating the information to ground-based telescopes.

Conversely, the SVOM mission may react to alerts generated by transient sky observatories, on the ground or in space. SVOM will thus be a partner of choice for other observational programs, such as IceCube and its neutrino telescope, LIGO and Virgo for the detection of gravitational waves, LSST and SKA for transient sky in the visible and radio range.

Gravitational waves

Observation programs

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Author : CEA / Irfu & Jesse Palmerio

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.

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Author : CEA / Irfu & Jesse Palmerio

The transient sky

If the heart of the SVOM mission is to guarantee the observation of approximately one hundred gamma-ray bursts per year, it is above all a formidable tool designed to scrutinize the transient sky as a whole.

Transient phenomena

Various astronomical objects are called « transient » because they change over time. These changes are distinguished in particular by a variation in their luminosity or their observed position and can be caused by movement or by transformation of the source itself. The time scales of transient phenomena are diverse,  from seconds, to hours or days, and require appropriate observational strategies. Gamma-ray bursts are among the most studied transient phenomena, but there are many others, such as supernovae, eruptive stars (mostly red dwarfs and potentially some brown dwarfs) or active galactic nuclei.

Artist's view of a very violent eruption on one of the red dwarfs of the couple of DG Canum Venaticorum or DG CVn, located about 60 light years from the Solar System. On April 23, 2014, the Swift satellite's BAT (Burst Alert Telescope) instrument gave the alert for a thorough observing campaign. Credit: NASA, Goddard Space Flight Center, S. Wiessinger

Artist’s view of a very violent eruption on one of the red dwarfs of the couple of DG Canum Venaticorum or DG CVn, located about 60 light years from the Solar System. On April 23, 2014, the Swift satellite’s BAT (Burst Alert Telescope) instrument gave the alert for a thorough observing campaign. Credit: NASA, Goddard Space Flight Center, S. Wiessinger

This field of ​​research is rapidly expanding and it could yield potential discoveries on the physics associated with violent cosmic phenomena . However, this requires significant detections and monitoring devices. SVOM is able to meet these expectations.

Like its sister mission SWIFT developed by NASA, SVOM includes in its program significant room for non-gamma-ray burst related science. The field of gamma-ray observation is rich in transient events. Sweeping the sky with its multi-wavelength instruments, SVOM can issue an alert following the detection of transient phenomena, communicating the information to ground-based telescopes.

Conversely, the SVOM mission may react to alerts generated by transient sky observatories, on the ground or in space. SVOM will thus be a partner of choice for other observational programs, such as IceCube and its neutrino telescope, LIGO and Virgo for the detection of gravitational waves, LSST and SKA for transient sky in the visible and radio range.

Gravitational waves

Observation programs

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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.

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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)

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Author : CEA / Irfu

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…

 

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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)

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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.

 

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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 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.

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Author : CEA / Irfu & Olivier Godet

GRM (Gamma Ray burst Monitor)

The GRM with a total FoV of 2.6 sr consists of three detectors called GRDs (Gamma-Ray Detectors). The GRM will provide information on the spectral shape and the lightcurve of GRBs during the prompt phase in the 15 keV – 5 MeV energy range. Each GRD is made of a 200 cm2 and 1.5 cm thick NaI scintillator coupled with a photomultiplier (PM). Incident photons deposit within the NaI crystal some energy that is then transformed into optical radiation. This latter radiation hits the PM photocathode generating electrons that will be multiplied within the PM in order to create a measurable output signal. The GRM also includes a radioactive source emitting in Gamma-rays for calibration purposes.

GRM2

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

The three GRDs are inclined by 30° with respect to ECLAIRs pointing axis and are placed at the corners of an equilateral triangle  (see the above Figure). Information from the 3 GRDs can be used together to localize GRBs within a FoV larger than that of ECLAIRs, with a 15°x15° accuracy. The GRM will help search for electromagnetic events coincidental with gravitational wave events detected on the ground. The GRM is expected to detect GRBs at a rate of around a hundred events per year.

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Author : CEA / Irfu & Olivier Godet

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.

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Author : CEA / Irfu & Emanuele Perinati

The Visible Telescope (VT)

The Visible Telescope (VT) will observe the visible component of the GRB afterglows. Having a total spectral coverage from 400 to 1000 nm, the VT is also sensitive in the near-infrared band.

VT

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

The VT is a Ritchey-Chretien telescope with a 40 cm primary mirror and a field of view of 26 x 26 arcmin. Its focal plane is equipped with two 2048 × 2048 pixel CCD cameras covering two different wavelength ranges: the blue channel works from 450 to 650 nm and the red channel from 650 to 1000 nm. The VT will be able to detect a source of 22.5 visual magnitude in 300 seconds. Furthermore, using the refined position provided by the MXT, the VT will allow to reconstruct the position of the GRBs with an accuracy of a few arcseconds in less than 10 min after the alerts given by the ECLAIRS.  The VT is expected to detect and locate about 60 GRBs per year.

 

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Author : CEA / Irfu & Emanuele Perinati

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 at very high frequency (VHF) in radio by an onboard antenna. The message is then downlinked through a network of radio stations spread around the Earth’s equator.

Carte du réseau d'alerte

Map showing the approximate locations of the VHF antenna network – Credit: CNES/CNRS/CEA/Irfu

At least 43 VHF antennae will be homogeneously deployed in the inter-tropical zone around the Earth. 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 that will refine the GRB position. A summary of the GFT results will then be sent back to the FSC in order to share their findings with large observing facilities. If everything goes smoothly, it should take less than 4 min to start acquiring GRB optical spectra with large telescopes.

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Author : CEA / Irfu & Olivier Godet

GWAC (Ground-based Wide Angle Camera)

The main science objective of the Ground-based Wide Angle Camera (GWAC) is to observe  in optical (between 500 and 860 nm) the prompt emission of GRBs detected by ECLAIRs. The GWAC will consist of 36 Ø180mm cameras, totalling a FoV of ~5000 degrees2 i.e. roughly half of ECLAIRs FoV. Each camera will be equipped with a 4096×4096 E2V CCD.

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GWAC

Engineering model of one GWAC module (4 cameras). The GWAC, once completed, will consist of 36 cameras. The first light is expected  in 2017. Credit: NAOC

The GWAC cameras will enable a systematic study of any optical emission prior to and during the  high-energy prompt emission phase reaching a 10s sensitivity of ~16 mag. in the V band. The characteristics of the GWAC are such that it will be a powerful tool to study the transient sky and to look for optical counterparts of gravitational wave events.

Two 60cm diameter telescopes and a network of 30cm diameter telescopes will complete the GWAC system. These robotic telescopes will promptly react to any transient source detected by the GWAC cameras and will help validating the detection.

The GWAC will be divided into two sub-sets, each of them consisting of 18 cameras and a Ø60cm  follow-up telescope. One part will be installed at CTIO in Chili and the other part at the ALI observatory in the west of Tibet.

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Author : CEA / Irfu & Olivier Godet

GFT (Ground Follow-up Telescope)

The robotic Ground Follow-up Telescopes (GFT) play a crucial role in observing and studying Gamma-Ray Bursts (GRBs).

When an alert is received from the VHF network, these telescopes promptly (within 1 min following the onboard ECLAIRs trigger) repoint towards the GRB position to start observing and search for a GRB optical/near-infrared counterpart. These follow-up telescopes measure GRB positions with accuracies typically around 1 arcsecond and provide a flux sampling over time of the GRB afterglow emission in several bands (from optical to near infrared). They also measure crude estimates of the GRB redshift (i.e. its distance from Earth).

All the GFT results are then sent to the French Science Center (FSC) that will dispatch the alert messages to larger facilities like the NTT and the VLT in optical or ALMA in radio.

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.

In addition to the science payload in space, SVOM will include two follow-up telescopes composed of a primary mirror of at least 1 meter in diameter : one located at San Pedro Martir in Mexico under French responsability and another one at the Xinglong Observatory under Chinese responsability.

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Author : CEA - LAM & Olivier Godet

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.

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Author : CEA / Irfu & Olivier Godet