arXiv subjects

Jean-Luc Atteia

Publications and source records attributed to Jean-Luc Atteia.

36 records · Page 2Linked to original sources

arXiv2016

Investigating the impact of optical selection effects on observed rest frame prompt GRB properties

Measuring gamma-ray burst (GRB) properties in their rest-frame is crucial to understand the physics at work in gamma-ray bursts. This can only be done for GRBs with known redshift. Since redshifts are usually measured from the optical spectrum of the afterglow, correlations between prompt and afterglow emissions may introduce biases in the distribution of rest-frame properties of the prompt emission. Our analysis is based on a sample of 90 GRBs with good optical follow-up and well measured prompt emission. 76 of them have a measure of redshift and 14 have no redshift. We estimate their optical brightness with their R magnitude measured two hours after the trigger and compare the rest frame prompt properties of different classes of GRB afterglow brightness. We find that the optical brightness of GRBs in our sample is mainly driven by their intrinsic afterglow luminosity. We show that GRBs with low and high afterglow optical fluxes have similar Epi , Eiso , Liso , indicating that the rest-frame distributions computed from GRBs with a redshift are not significantly distorted by optical selection effects. However we found that the rest frame T90 distribution is not immune to optical selection effect, which favor the selection of GRBs with longer durations. Finally, we note that GRBs in the upper part of the Epi-Eiso plane have fainter optical afterglows and we show that optical selection effects strongly favor the detection of GRBs with bright afterglows located close or below the best-fit Epi-Eiso relation, whose redshift is easily measurable.

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arXiv2015

The ECLAIRs GRB-trigger telescope on-board the future mission SVOM

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is an approved satellite mission for Gamma-Ray Burst (GRB) studies, developed in cooperation between the Chinese National Space Agency (CNSA), the Chinese Academy of Sciences (CAS), the French Space Agency (CNES) and French laboratories. SVOM entered Phase B in 2014 and is scheduled for launch in 2021. SVOM will provide fast and accurate GRB localizations, and determine the temporal and spectral properties of the GRB emission, thanks to a set of 4 on-board instruments. The trigger system of the coded-mask telescope ECLAIRs images the sky in the 4-120 keV energy range, in order to detect and localize GRBs in its 2 sr-wide field of view. The low-energy threshold of ECLAIRs is well suited for the detection of highly redshifted GRB. The high-energy coverage is extended up to 5 MeV thanks to the non-imaging gamma-ray spectrometer GRM. GRB alerts are sent in real-time to the ground observers community, and a spacecraft slew is performed in order to place the GRB within the field of view of the soft X-ray telescope MXT and the visible-band telescope VT, to refine the GRB position and study its early afterglow. The ground-based robotic telescopes GFTs and the wide angle cameras GWAC complement the on-board instruments. In this paper we present the ECLAIRs soft gamma-ray imager which will provide the GRB triggers on-board SVOM.

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arXiv2013

The Hot and Energetic Universe: A White Paper presenting the science theme motivating the Athena+ mission

This White Paper, submitted to the recent ESA call for science themes to define its future large missions, advocates the need for a transformational leap in our understanding of two key questions in astrophysics: 1) How does ordinary matter assemble into the large scale structures that we see today? 2) How do black holes grow and shape the Universe? Hot gas in clusters, groups and the intergalactic medium dominates the baryonic content of the local Universe. To understand the astrophysical processes responsible for the formation and assembly of these large structures, it is necessary to measure their physical properties and evolution. This requires spatially resolved X-ray spectroscopy with a factor 10 increase in both telescope throughput and spatial resolving power compared to currently planned facilities. Feedback from supermassive black holes is an essential ingredient in this process and in most galaxy evolution models, but it is not well understood. X-ray observations can uniquely reveal the mechanisms launching winds close to black holes and determine the coupling of the energy and matter flows on larger scales. Due to the effects of feedback, a complete understanding of galaxy evolution requires knowledge of the obscured growth of supermassive black holes through cosmic time, out to the redshifts where the first galaxies form. X-ray emission is the most reliable way to reveal accreting black holes, but deep survey speed must improve by a factor ~100 over current facilities to perform a full census into the early Universe. The Advanced Telescope for High Energy Astrophysics (Athena+) mission provides the necessary performance (e.g. angular resolution, spectral resolution, survey grasp) to address these questions and revolutionize our understanding of the Hot and Energetic Universe. These capabilities will also provide a powerful observatory to be used in all areas of astrophysics.

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arXiv2013

The Hot and Energetic Universe: Luminous extragalactic transients

We discuss the importance and potential contribution of Athena+ to the science questions related to gamma-ray bursts, tidal disruption events and supernova shock break-out. Athena+ will allow breakthrough observations involving high-resolution X-ray spectroscopic observations of high-z gamma-ray bursts, observations of tidal disruption events tailored to determine the mass and potentially the spin of the black hole responsible for the tidal disruption and observations of X-rays from the supernova shock breakout providing a measure of the radius of the exploding star or of the companion in the case of type Ia supernovae. We briefly discuss survey facilities that will provide triggers to these events envisaged to be operational around 2028.

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arXiv2013

Gamma-Ray Bursts, witnessing the birth of stellar mass black holes

Gamma-ray bursts are associated with catastrophic cosmic events. They appear when a new black hole, created after the explosion of a massive star or the merger of two compact stars, quickly accretes the matter around it and ejects a transient relativistic jet in our direction. This review discusses the various types of gamma-ray bursts, their progenitors, their beaming and their rate in the local universe. We emphasize the broad astrophysical interest of GRB studies, and the crucial role of high-energy satellites as exclusive suppliers of GRB alerts and initial locations.

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arXiv2011

Observing the prompt emission of gamma-ray bursts

Gamma-ray bursts (GRBs) were first detected thanks to their prompt emission, which was the only information available for decades. In 2010, while the high-energy prompt emission remains the main tool for the detection and the first localization of GRB sources, our understanding of this crucial phase of GRBs has made great progress. We discuss some recent advances in this field, like the occasional detection of the prompt emission at all wavelengths, from optical to GeV; the existence of sub-luminous GRBs; the attempts to standardize GRBs; and the possible detection of polarization in two very bright GRBs. Despite these advances, tantalizing observational and theoretical challenges still exist, concerning the detection of the faintest GRBs, the panchromatic observation of GRBs from their very beginning, the origin of the prompt emission, or the understanding of the physics at work during this phase. Significant progress on this last topic is expected with SVOM thanks to the observation of dozens of GRBs from optical to MeV during the burst itself, and the measure of the redshift for the majority of them. SVOM will also change our view of the prompt GRB phase in another way. Within a few years, the sensitivity of sky surveys at optical and radio frequencies, and outside the electromagnetic domain in gravitational waves or neutrinos, will allow them to detect several new types of transient signals, and SVOM will be uniquely suited to identify which of these transients are associated with GRBs. This radically novel look at GRBs may elucidate the complex physics producing these bright flashes.

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arXiv2008

Multiple Component Analysis of Time Resolved Spectra of GRB041006: A Clue to the Nature of Underlying Soft Component of GRBs

GRB 041006 was detected by HETE-2 at 12:18:08 UT on 06 October 2004. This GRB displays a soft X-ray emission, a precursor before the onset of the main event, and also a soft X-ray tail after the end of the main peak. The light curves in four different energy bands display different features; At higher energy bands several peaks are seen in the light curve, while at lower energy bands a single broader bump dominates. It is expected that these different features are the result of a mixture of several components each of which has different energetics and variability. To reveal the nature of each component, we analysed the time resolved spectra and they are successfully resolved into several components. We also found that these components can be classified into two distinct classes; One is a component which has an exponential decay of $E_{p}$ with a characteristic timescale shorter than $\sim$ 30 sec, and its spectrum is well represented by a broken power law function, which is frequently observed in many prompt GRB emissions, so it should have an internal-shock origin. Another is a component whose $E_{p}$ is almost unchanged with characteristic timescale longer than $\sim$ 60 sec, and shows a very soft emission and slower variability. The spectrum of the soft component is characterized by either a broken power law or a black body spectrum. This component might originate from a relatively wider and lower velocity jet or a photosphere of the fireball. By assuming that the soft component is a thermal emission, the radiation radius is initially $4.4 \times 10^{6}$ km, which is a typical radius of a blue supergiant, and its expansion velocity is $2.4 \times 10^{5}$ km/s in the source frame.

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arXiv2007

A Comprehensive Study of Short Bursts from SGR 1806-20 and SGR 1900+14 Detected by HETE-2

We present the results of temporal and spectral studies of the short burst (less than a few hundred milliseconds) from the soft gamma repeaters (SGRs) 1806-20 and 1900+14 using the HETE-2 samples. In five years from 2001 to 2005, HETE-2 detected 50 bursts which were localized to SGR 1806-20 and 5 bursts which were localized to SGR 1900+14. Especially SGR 1806-20 was active in 2004, and HETE-2 localized 33 bursts in that year. The cumulative number-intensity distribution of SGR 1806-20 in 2004 is well described by a power law model with an index of -1.1+/-0.6. It is consistent with previous studies but burst data taken in other years clearly give a steeper distribution. This may suggest that more energetic bursts could occur more frequently in periods of greater activity. A power law cumulative number-intensity distribution is also known for earthquakes and solar flares. It may imply analogous triggering mechanisms. Although spectral evolution during bursts with a time scale of > 20 ms is not common in the HETE-2 sample, spectral softening due to the very rapid (< a few milliseconds) energy reinjection and cooling may not be excluded. The spectra of all short bursts are well reproduced by a two blackbody function (2BB) with temperatures ~4 and ~11 keV. From the timing analysis of the SGR 1806-20 data, a time lag of 2.2+/-0.4 ms is found between the 30-100 keV and 2-10 keV radiation bands. This may imply (1) a very rapid spectral softening and energy reinjection, (2) diffused (elongated) emission plasma along the magnetic field lines in pseudo equilibrium with multi-temperatures, or (3) a separate (located at < 700 km) emission region of softer component (say, ~4 keV) which could be reprocessed X-rays by higher energy (> 11 keV) photons from an emission region near the stellar surface.

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arXiv2007

HETE-2 Observations of the X-Ray Flash XRF 040916

A long X-ray flash was detected and localized by the instruments aboard the High Energy Transient Explorer II (HETE-2) at 00:03:30 UT on 2004 September 16. The position was reported to the GRB Coordinates Network (GCN) approximately 2 hours after the burst. This burst consists of two peaks separated by 200 s, with durations of 110 s and 60 s. We have analyzed the energy spectra of the 1st and 2nd peaks observed with the Wide Field X-Ray Monitor (WXM) and the French Gamma Telescope (FREGATE). We discuss the origin of the 2nd peak in terms of flux variabilities and timescales. We find that it is most likely part of the prompt emission, and is explained by the long-acting engine model. This feature is similar to some bright X-ray flares detected in the early afterglow phase of bursts observed by the Swift satellite.

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arXiv2007

Constraining the rate of GRB visible afterglows with the CFHTLS Very Wide Survey

We analyze images of the CFHTLS Very Wide Survey to search for visible orphan afterglows from gamma-ray bursts (GRBs). We have searched 490 square degrees down to magnitude r'=22.5 for visible transients similar to GRB afterglows. We translate our observations into constraints on the number of GRB visible afterglows in the sky, by measuring the detection efficiency of our search with a simulation reproducing the characteristics of our observational strategy and the properties of on-axis GRB afterglows. We have found only three potential candidates, of which two are most probably variable stars, and one presents similarities to an orphan afterglow. We constrain the number of visible afterglows to be less than 220 down to r'=22.5 in the whole sky at any time. Our observations are marginally consistent with the most optimistic model, which predicts orphan afterglows to be about 10 times more frequent than GRBs. This search has led to the detection of one possible GRB afterglow, and provides the strongest constraints on the rate of GRB visible afterglows as well as an estimation of the observing time required to detect a significant number of GRB afterglows.

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arXiv2007

The CFHTLS Real Time Analysis System "Optically Selected GRB Afterglows"

We describe a wide and deep search for optical GRB afterglows on images taken with MegaCAM at the Canada France Hawaii Telescope, within the framework of the CFHT Legacy Survey. This search is performed in near real-time thanks to a Real Time Analysis System called "Optically Selected GRB Afterglows", which has been completely realized and installed on a dedicated computer in Hawaii. This pipeline automatically and quickly analyzes Megacam images and extracts from them a list of astrometrically and photometrically variable objects which are displayed on a web page for validation by a member of the collaboration. In this paper, we comprehensively describe the RTAS process. We also present statistical results based on nearly one full year of operation, showing the quality of the images and the performance of the RTAS. Finally, we compare the efficiency of this study with similar searches, propose an ideal observational strategy using simulations, and discuss general considerations on the searches for GRB afterglows independently of the prompt emission. This is the first of a series of two papers. A second paper will discuss the characterization of variable objects we have found, as well as the GRB afterglow candidates and their nature. We will also estimate or at least constrain the collimation factor of GRB using the totality of the Very Wide Survey observations.

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arXiv2006

An Optically Dark GRB Observed by HETE-2: GRB 051022

GRB 051022 was detected at 13:07:58 on 22 October 2005 by HETE-2. The location of GRB 051022 was determined immediately by the flight localization system. This burst contains multiple pulses and has a rather long duration of about 190 seconds. The detections of candidate X-ray and radio afterglows were reported, whereas no optical afterglow was found. The optical spectroscopic observations of the host galaxy revealed the redshift z = 0.8. Using the data derived by HETE-2 observation of the prompt emission, we found the absorption N_H = 8.8 -2.9/+3.1 x 10^22 cm^-2 and the visual extinction A_V = 49 -16/+17 mag in the host galaxy. If this is the case, no detection of any optical transient would be quite reasonable. The absorption derived by the Swift XRT observations of the afterglow is fully consistent with those obtained from the early HETE-2 observation of the prompt emission. Our analysis implies an interpretation that the absorbing medium could be outside external shock at R ~ 10^16 cm, which may be a dusty molecular cloud.

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arXiv2006

Continuous optical monitoring during the prompt emission of GRB 060111B

We present the time-resolved optical emission of GRB 060111B during its prompt phase, measured with the TAROT robotic observatory. This is the first time that the optical emission from a gamma-ray burst has been continuously monitored with a temporal resolution of a few seconds during the prompt gamma-ray phase. The temporal evolution of the prompt optical emission at the level of several seconds is used to provide a clue to the origin of this emission. The optical emission was found to decay steadily from our first measure, 28s after the trigger, in contrast to the gamma-ray emission, which exhibits strong variability at the same time. This behaviour strongly suggests that the optical emission is due to the reverse shock.

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arXiv2006

Optically Selected GRB Afterglows

Since November 2004, we attempt to detect GRB optical afterglows in near real-time on images taken at the Canada France Hawaii Telescope within the Very Wide Survey, component of the CFHT Legacy survey. To do so, a Real Time Analysis System automatically and quickly analyzes MegaCAM images and extracts from them a list of photometrically and astrometrically variable objects which is then validated by a member of the collaboration. Each month, we repeatedly observe 15 to 30 square degrees down to magnitude i' = 22.5. A few objects are classified as candidates and analyzed more deeply, and statistics are done showing the treatment's performance.

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arXiv2006

An improved redshift indicator for Gamma-Ray Bursts, based on the prompt emission

We propose an improved version of the redshift indicator developed by Atteia (2003), which gets rid of the dependence on the burst duration and provides better estimates for high-redshift GRBs. We present the derivation and the definition of this redshift indicator, then its calibration with 17 GRBs with known redshifts detected by HETE-2 and 2 more detected by Konus-Wind. We also provide an estimation of the redshift for 59 bursts, and we finally discuss the redshift distribution of HETE-bursts and the possible other applications of this redshift indicator.

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arXiv2006

Optically Selected GRB Afterglows, a Real Time Analysis System at the CFHT

We attempt to detect optical GRB afterglows on images taken by the Canada France Hawaii Telescope for the Very Wide survey, component of the Legacy Survey. To do so, a Real Time Analysis System called "Optically Selected GRB Afterglows" has been installed on a dedicated computer in Hawaii. This pipeline automatically and quickly analyzes Megacam images and extracts from them a list of variable objects which is displayed on a web page for validation by a member of the collaboration. The Very Wide survey covers 1200 square degrees down to i'=23.5. This paper briefly explain the RTAS process.

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arXiv2003

On the nature of X-ray Flashes

We have developed a toy model for internal shocks which has been used to generate a large number of synthetic GRBs in order to find in the parameter space the conditions which can lead to the formation of X-ray flashes. The key condition appears to be a small contrast of the Lorentz factor in the relativistic wind emitted by the central engine.

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arXiv2002

Observational constraints on the afterglow of GRB 020531

We present the data acquired by the TAROT automated observatory on the afterglow of GRB 020531. Up to now, no convincing afterglow emission has been reported for this short/hard GRB at any wavelength, including X-ray and optical. The combination of our early limits, with other published data allows us to put severe constraints on the afterglow magnitude and light curve. The limiting magnitude is 18.5 in R band, 88 minutes after the GRB, and the decay slope power law index could be larger than 2.2.

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