arXiv subjects

J. -P. Dezalay

Publications and source records attributed to J. -P. Dezalay.

At least 19 recordsLinked to original sources

arXiv2026

ECLAIRs: the SVOM high-energy transient trigger camera

The core instrument of the SVOM Gamma-ray burst mission launched in June 2024 is the 4-150 keV 2-D coded mask camera ECLAIRs responsible for the autonomous trigger and localization of transient events within its field of view. The flight model of ECLAIRs has been built by several French labs (IRAP, CEA, APC) under the supervision of the French Space Agency (CNES), while APC, LUPM and IAP built a suite of data reduction and analysis software. This paper outlines the main science goals of ECLAIRs and describes the different instrument sub-systems and their main characteristics. The paper then discusses the instrument configuration and operation as well as the main in-flight measured performances. Finally, the paper summarizes the science performance of ECLAIRs up to March 31, 2025.

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arXiv2026

SVOM/ECLAIRs detection plane: main features and performance

The detection plane of the high-energy transient camera ECLAIRs onboard SVOM is made of 200 XRDPIX detection modules, each consisting of a matrix of $8\times 4$ Schottky-type CdTe detectors hybridized with the low-noise and low-consumption ASIC IDeF-X. The 6400 detectors are operated at -20°C and reverse biased at -300 V, reaching a low energy threshold of 4 keV. The 20 us time resolution readout electronics works in photon counting mode classifying detected events as single or multiple events and measuring the deposited energy in real time. In this paper, we present the detection plane sub-systems and their main features. We also discuss its overall performances as measured both on ground and in-flight, showing compliance with the ECLAIRs science requirements.

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arXiv2026

The GRB joint scientific analysis pipeline of the ECLAIRs and GRM instruments on board SVOM

The study of the prompt high-energy emission of Gamma-Ray Bursts (GRBs) with SVOM relies on the observations performed by ECLAIRs (4-150 keV) and the Gamma-Ray Monitor (GRM, 0.015-5 MeV), the two wide field-of-view instruments on board the satellite. In this article, we introduce the eclgrm pipelines running at the French Science Center of SVOM, which combine the ECLAIRs and GRM data to generate scientific data products describing the GRB broad-band temporal and spectral properties. The architecture of the pipelines is presented, as well as their activation following each onboard trigger, and their workflow. The statistical data analysis methods employed by the pipelines are described, along with the scientific data products that are created in real time or from the full event data. We also present the eclgrm-ui user interface which allows the scientists on shift to monitor the automated data processings in the pipelines, and to optimize the analysis results interactively.

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arXiv2019

Designing large pixelated CdTe detection planes for hard X-ray transients detection

We discuss the need for very large detection planes for the detection of hard X-ray transients in the multi-messenger era that started with the quasi-simultaneous detection of GRB~170817A by \textit{Fermi}/GBM and \textit{INTEGRAL}/SPI on one hand and the gravitational waves event GW 170817, detected by the LVC collaboration, on the other hand. Then, we present a brief survey of current and future instruments and their expected sensitivity, pointing the fact that the gain in the number of GRBs is achieved by future projects thanks to their larger field of view rather than to their larger effective area. Based on our experience with \textit{SVOM}/ECLAIRs, we then address various problems associated with the realization of very large detection planes (\mbox{$\ge 1 \mathrm m^{2}$}), and we demonstrate that CdTe detectors are well suited for this task. We conclude with a discussion of some key parameters that must be taken into account in the realization of instruments based on these detectors. We hope that this paper will motivate the elaboration of detailed proposals of large area wide-field hard X-ray monitors that will be crucially needed in the next decade.

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arXiv2017

The maximum isotropic energy of gamma-ray bursts

The most energetic gamma-ray bursts (GRBs) are remarkable sources releasing huge amounts of energy on short timescales. Their prompt emission, which usually lasts few seconds, is so bright that it is visible across the whole observable universe. Studying these extreme events may provide clues on the nature of GRB progenitors and on the physical processes at work in relativistic jets. In this paper, we study the bright end of the isotropic energy distribution of long GRBs. We use two samples of long GRBs with redshift detected by Fermi/GBM or Konus-Wind, two instruments which measure the spectral shape and the energetics of the prompt emission accurately. We focus on GRBs within a range of redshifts z = 1 -- 5, a volume that contains a large number of energetic GRBs, and we propose a simple method to reconstruct the bright end of the GRB energy distribution from the observed one. We find that the GRB energy distribution cannot be described by a simple power law but requires a strong cutoff above $1-3 \times 10^{54}$ erg. We attribute this feature to an intrinsic limit on the energy per unit of solid angle radiated by gamma-ray bursts.

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arXiv2017

Comparing the birth rate of stellar black holes in binary black hole mergers and long GRBs

Gravitational wave interferometers have proved the existence of a new class of binary black holes (BBHs) weighting tens of solar masses and they have provided the first reliable measurement of the rate of coalescing black holes (BHs) in the local universe. On another side, long gamma-ray bursts (GRBs) detected with gamma-ray satellites are believed to be associated with the birth of stellar mass BHs, providing a measure of the rate of these events across the history of the universe, thanks to the measure of their cosmological redshift. These two types of sources, which are subject to different detection biases and involve BHs born in different environments with potentially different characteristics, provide complementary information on the birth rate of stellar BHs. We compare here the birth rates of BHs found in BBH mergers and in long GRBs. We construct a simple model which makes reasonable assumptions on the history of GRB formation, and which takes into account some major uncertainties, like the beaming angle of GRBs or the delay between the formation of BBHs and their coalescence. We use this model to evaluate the ratio of the number of stellar mass BHs formed in BBH mergers to those formed in GRBs. We find that in our reference model the birth rate of stellar BHs in BBH mergers represents from few percent to 100% of the rate of long GRBs and that comparable birth rates are favored by models with moderate beaming angles. We briefly discuss this result in view of our understanding of the progenitors of GRBs and BBH mergers, and we emphasize that this ratio, which will be better constrained in the coming years, can be directly compared with the prediction of stellar evolution models if a single model is used to produce GRBs and of BBH mergers with the same assumptions.

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arXiv2015

Connecting Prompt and Afterglow GRB emission I. Investigating the impact of optical selection effects in the Epi - Eiso plane

Measuring 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, especially considering that we measure the redshift of only one third of Swift GRBs. In this paper we study the brightness of optical GRB afterglows and the role of optical selection effects in the distribution of various intrinsic properties of GRBs and on the Epi - Eiso relation discovered by Amati et al. (2002). Our analysis is based on a sample of 85 GRBs with good optical follow-up and well measured prompt emission. 71 of them have a measure of redshift and 14 have no redshift. We discuss the connection between the location of GRBs in the Epi-Eiso plane and their optical brightness measured two hours after the trigger in the GRB rest frame. We show that the brightness of GRBs in our sample is mainly driven by their intrinsic luminosity and depends only slightly on their redshift. We also show that GRBs with faint afterglows are preferentially located in the upper part of the Epi-Eiso plane. This optical selection effect favors the detection of GRBs with bright afterglows located below the best fit Epi - Eiso relation whose redshift is easily measurable. We conclude that the distributions of prompt GRB properties in the rest frame undergo selection effects due to the need to measure the redshift from the optical afterglow emission. These biases put significant uncertanties when interpreting the statistical studies of GRB properties in the rest frame. We show that the Epi - Eiso relation is not immune to these selection effects.

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arXiv2010

Spectral Lag Relations in GRB Pulses Detected with HETE-2

Using a pulse-fit method, we investigate the spectral lags between the traditional gamma-ray band (50-400 keV) and the X-ray band (6-25 keV) for 8 GRBs with known redshifts (GRB 010921, GRB 020124, GRB 020127, GRB 021211, GRB 030528, GRB 040924, GRB 041006, GRB 050408) detected with the WXM and FREGATE instruments aboard the HETE-2 satellite. We find several relations for the individual GRB pulses between the spectral lag and other observables, such as the luminosity, pulse duration, and peak energy (Epeak). The obtained results are consistent with those for BATSE, indicating that the BATSE correlations are still valid at lower energies (6-25 keV). Furthermore, we find that the photon energy dependence for the spectral lags can reconcile the simple curvature effect model. We discuss the implication of these results from various points of view.

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arXiv2006

X-ray Flashes or soft Gamma-ray Bursts? The case of the likely distant XRF 040912

In this work, we present a multi-wavelength study of XRF 040912, aimed at measuring its distance scale and the intrinsic burst properties. We performed a detailed spectral and temporal analysis of both the prompt and the afterglow emission and we estimated the distance scale of the likely host galaxy. We then used the currently available sample of XRFs with known distance to discuss the connection between XRFs and classical Gamma-ray Bursts (GRBs). We found that the prompt emission properties unambiguously identify this burst as an XRF, with an observed peak energy of E_p=17+/-13 keV and a burst fluence ratio S(2-30keV)/S(30-400keV)>1. A non-fading optical source with R~24 mag and with an apparently extended morphology is spatially consistent with the X-ray afterglow, likely the host galaxy. XRF 040912 is a very dark burst since no afterglow optical counterpart is detected down to R>25 mag (3 sigma limiting magnitude) at 13.6 hours after the burst. The host galaxy spectrum detected from 3800A to 10000A, shows a single emission line at 9552A. The lack of any other strong emission lines blue-ward of the detected one and the absence of the Ly alpha cut-off down to 3800A are consistent with the hypothesis of the [OII] line at redshift z=1.563+/-0.001. The intrinsic spectral properties rank this XRF among the soft GRBs in the E_peak-E_iso diagram. Similar results were obtained for most XRFs at known redshift. Only XRF 060218 and XRF 020903 represent a good example of instrinsic XRF(i-XRF) and are possibly associated with a different progenitor population. This scenario may calls for a new definition of XRFs.

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arXiv2006

HETE-2 Localizations and Observations of Four Short Gamma-Ray Bursts: GRBs 010326B, 040802, 051211 and 060121

Here we report the localizations and properties of four short-duration GRBs localized by the High Energy Transient Explorer 2 satellite (HETE-2): GRBs 010326B, 040802, 051211 and 060121, all of which were detected by the French Gamma Telescope (Fregate) and localized with the Wide-field X-ray Monitor (WXM) and/or Soft X-ray Camera (SXC) instruments. We discuss eight possible criteria for determining whether these GRBs are "short population bursts" (SPBs) or "long population bursts" (LPBs). These criteria are (1) duration, (2) pulse widths, (3) spectral hardness, (4) spectral lag, (5) energy Egamma radiated in gamma rays (or equivalently, the kinetic energy E_KE of the GRB jet), (6) existence of a long, soft bump following the burst, (7) location of the burst in the host galaxy, and (8) type of host galaxy. In particular, we have developed a likelihood method for determining the probability that a burst is an SPB or a LPB on the basis of its T90 duration alone. A striking feature of the resulting probability distribution is that the T90 duration at which a burst has an equal probability of being a SPB or a LPB is T90 = 5 s, not T90 = 2 s, as is often used. All four short-duration bursts discussed in detail in this paper have T90 durations in the Fregate 30-400 keV energy band of 1.90, 2.31, 4.25, and 1.97 sec, respectively, yielding probabilities P(S|T90) = 0.97, 0.91, 0.60, and 0.95 that these bursts are SPBs on the basis of their T90 durations alone. All four bursts also have spectral lags consistent with zero. These results provide strong evidence that all four GRBs are SPBs (abstract continues).

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arXiv2005

HETE-2 Observation of two gamma-ray bursts at z > 3

GRB 020124 and GRB 030323 constitute half the sample of gamma-ray bursts with a measured redshift greater than 3. This paper presents the temporal and spectral properties of these two gamma-ray bursts detected and localized with HETE-2. While they have nearly identical redshifts (z=3.20 for GRB 020124, and z=3.37 for GRB 030323), these two GRBs span about an order of magnitude in fluence, thus sampling distinct regions of the GRB luminosity function. The properties of these two bursts are compared with those of the bulk of the GRB population detected by HETE-2. We also discuss the energetics of GRB 020124 and GRB 030323 and show that they are compatible with the Epeak - Eiso relation discovered by Amati et al. (2002). Finally, we compute the maximum redshifts at which these bursts could have been detected by HETE-2 and we address various issues connected with the detection and localization of high-z GRBs.

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arXiv2004

HETE Observations of the Gamma-Ray Burst GRB030329: Evidence for an Underlying Soft X-ray Component

An exceptionally intense gamma-ray burst, GRB030329, was detected and localized by the instruments on board the High Energy Transient Explorer satellite (HETE) at 11:37:14 UT on 29 March 2003. The burst consisted of two \~10s pulses of roughly equal brightness and an X-ray tail lasting >100s. The energy fluence in the 30-400 keV energy band was 1.08e-4 erg/cm2, making GRB030329 one of the brightest GRBs ever detected. Communication of a 2 arcmin error box 73 minutes after the burst allowed the rapid detection of a counterpart in the optical, X-ray, radio and the ensuing discovery of a supernova with most unusual characteristics. Analyses of the burst lightcurves reveal the presence of a distinct, bright, soft X-ray component underlying the main GRB: the 2-10 keV fluence of this component is ~7e-6 erg/cm2. The main pulses of GRB030329 were preceded by two soft, faint, non-thermal bumps. We present details of the HETE observations of GRB030329.

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arXiv2003

Scientific Highlights of the HETE-2 Mission

The HETE-2 mission has been highly productive. It has observed more than 250 GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has localized 43 GRBs to date. Twenty-one of these localizations have led to the detection of X-ray, optical, or radio afterglows, and as of now, 11 of the bursts with afterglows have known redshifts. HETE-2 has confirmed the connection between GRBs and Type Ic supernovae, a singular achievement and certainly one of the scientific highlights of the mission so far. It has provided evidence that the isotropic-equivalent energies and luminosities of GRBs are correlated with redshift, implying that GRBs and their progenitors evolve strongly with redshift. Both of these results have profound implications for the nature of GRB progenitors and for the use of GRBs as a probe of cosmology and the early universe. HETE-2 has placed severe constraints on any X-ray or optical afterglow of a short GRB. It is also solving the mystery of "optically dark' GRBs, and revealing the nature of X-ray flashes.

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arXiv2003

HETE-2 Localization and Observation of the Bright, X-Ray-Rich Gamma-Ray Burst GRB021211

A bright, x-ray-rich GRB was detected by HETE-2 at 11:18:34.03 UT on 11 Dec 2002. The WXM localization was to 14' and relayed to the GCN 22 s after the start of the burst. The ground SXC localization was within 2' of R.A. 08h 09m 00s, Dec 06d 44' 20" (J2000). GRB021211 consists of a single, FRED-like pulse with t90s of 2.3 s (85-400 keV) and 8.5 s (2-10 keV). The peak photon number and photon energy fluxes in the 2-400 keV band, are 34.0 +/- 1.8 ph cm^-2 s^-1 and 1.68 +/- 0.11 x 10^-6 erg cm^-2 s^-1, respectively. The energy fluences in the 2-30 keV and 30-400 kev energy bands are S_X = 1.36 +/- 0.05 x 10^-6 erg cm^-2 and S_gamma 2.17 +/- 0.15 x 10^-6 erg cm^-2, respectively. Thus GRB021211 is an X-ray-rich GRB (S_X/S_gamma = 0.63 > 0.32). The spectrum is well-fit by a Band function (alpha = -0.805, beta = -2.37, E_peak = 46.8 keV). The prompt localization allowed the detection of an optical afterglow for what would otherwise have been an ``optically dark'' GRB. GRB 021211 demonstrates that some fraction of burst afterglows are ``optically dark'' because their optical afterglows at times > 1 hr after the burst are very faint, and thus have often escaped detection. GRB 021211 shows that such ``optically dim'' bursts can have very bright afterglows at times < 20 min after the burst.

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arXiv2002

HETE-2 Localization and Observations of the Short, Hard Gamma-Ray Burst GRB020531

The {\it HETE-2} (hereafter \HETE) French Gamma Telescope (FREGATE) and the Wide-field X-ray Monitor (WXM) instruments detected a short ($t_{50} = 360$ msec in the FREGATE 85-300 keV energy band), hard gamma-ray burst (GRB) that occurred at 1578.72 SOD (00:26:18.72 UT) on 31 May 2002. The WXM flight localization software produced a valid location in spacecraft (relative) coordinates. However, since no on-board real-time star camera aspect was available, an absolute localization could not be disseminated. A preliminary localization was reported as a GCN Position Notice at 01:54:22 UT, 88 min after the burst. Further ground analysis produced a refined localization, which can be expressed as a 90% confidence rectangle that is 67 arcminutes in RA and 43 arcminutes in Dec (90% confidence region), centered at RA = +15$^{\rm h}$ 14$^{\rm m}$ 45$^{\rm s}$, Dec = -19$^\circ$ 21\arcmin 35\arcsec (J2000). An IPN localization of the burst was disseminated 18 hours after the GRB (Hurley et al. 2002b). A refined IPN localization was disseminated $\approx$ 5 days after the burst. This hexagonal-shaped localization error region is centered on RA = 15$^{\rm h}$ 15$^{\rm m}$ 03.57$^{\rm s}$, -19$^\circ$ 24\arcmin 51.00\arcsec (J2000), and has an area of $\approx$ 22 square arcminutes (99.7% confidence region). The prompt localization of this short, hard GRB by \HETE and the anti-Sun pointing of the \HETE instruments, coupled with the refinement of the localization by the IPN, has made possible rapid follow-up observations of the burst at radio, optical, and X-ray wavelengths.

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arXiv2001

Temporal and spectral gamma-ray properties of Mkn421 above 250 GeV from CAT observations between 1996 and 2000

The gamma-ray emission above 250 GeV from the BL Lac object Markarian 421 was observed by the CAT Cherenkov imaging telescope between December, 1996, and June, 2000. In 1998, the source produced a series of small flares, making it the second extragalactic source detected by CAT. The time-averaged differential spectrum has been measured from 0.3 to 5 TeV, which is well fitted with a power law with an index of -2.88+-0.12(stat)+-0.06(syst). In 2000, the source showed an unprecedented activity, with variability time-scales as short as one hour, as for instance observed during the night between 4 and 5 February. The 2000 time-averaged spectrum measured is compatible with that of 1998, but some indication of a spectral curvature is found between 0.3 and 5 TeV. The possibility of TeV spectral hardening during flares is also discussed, and the results are compared to those obtained on the other TeV BL Lac, Markarian 501.

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arXiv2000

Observations of the Soft Gamma-Ray early Afterglow emission from Two Bright Gamma-ray Bursts

We present the results of observations of the soft gamma-ray early afterglows with the energy above 100keV from two bright Gamma-ray bursts detected by the PHEBUS instrument of the GRANAT orbital observatory. We show that the light curves of GRB910402 and GRB920723 events present the afterglow emission with fading fluxes. During our observations ~700s for these gamma-ray bursts the afterglow emission was fading as the power law of time with indices equal to -0.70+/-0.04 and -0.60+/-0.05 (at 1sigma confidence level). In both cases just after the end of the GRB event we observed the energy spectrum of the afterglow emissions which was softer than the energy spectrum of the main GRB events. The average photon index of the main GRB event (in 100-800keV range) is equal to \~1.5. In the beginning of the afterglow emission the energy spectra of both events correspond to the much softer spectra with the photon index of ~2.5. We found that the times of abrupt softening of the burst spectra correspond within statistical errors to the moment when the afterglow emission begins to dominate over GRB emission. We found that during the afterglow emission of GRB910402 the statistically significant hardening of its spectra was observed. This is the first observation of hardening of GRB afterglow emission. Analysis of GRB910402 and its afterglow showed that this GRB source emits during ~700s of our observations in soft gamma-rays (100-500keV) only ~1.6% of its total energy released during the main event. For the GRB920723 we found that in afterglow during ~700s of our observations ~6% of the GRB total energy was released.

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arXiv2000

Very High Energy Gamma-ray spectral properties of Mrk 501 from CAT Cerenkov telescope observations in 1997

The BL Lac object Mrk 501 went into a very high state of activity during 1997, both in VHE gamma-rays and X-rays. We present here results from observations at energies above 250 GeV carried out between March and October 1997 with the CAT Cerenkov imaging Telescope. The average differential spectrum between 30 GeV and 13 TeV shows significant curvature and is well represented by phi_0 * E_TeV^{-(alpha + beta*log10(E_TeV))}, with: phi_0 = 5.19 +/- 0.13 {stat} +/- 0.12 {sys-MC} +1.66/-1.04 {sys-atm} * 10^-11 /cm^2/s/TeV alpha = 2.24 +/- 0.04 {stat} +/- 0.05 {sys} beta = 0.50 +/- 0.07 {stat} (negligible systematics). The TeV spectral energy distribution of Mrk 501 clearly peaks in the range 500 GeV-1 TeV. Investigation of spectral variations shows a significant hardness-intensity correlation with no measurable effect on the curvature. This can be described as an increase of the peak TeV emission energy with intensity. Simultaneous and quasi-simultaneous CAT VHE gamma-ray and BeppoSAX hard X-ray detections for the highest recorded flare on 16th April and for lower-activity states of the same period show correlated variability with a higher luminosity in X-rays than in gamma-rays. The observed spectral energy distribution and the correlated variability between X-rays and gamma-rays, both in amplitude and in hardening of spectra, favour a two-component emission scheme where the low and high energy components are attributed to synchrotron and inverse Compton (IC) radiation, respectively.

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