arXiv subjects

Laurent Bouchet

Publications and source records attributed to Laurent Bouchet.

14 recordsLinked to original sources

arXiv2026

Detection of Oscillations in a Type I X-Ray Burst of 4U 0614+091 with SVOM/ECLAIRs

On 2025 January 10, a thermonuclear (Type I) X-ray burst from the neutron star low-mass X-ray binary \textit{4U~0614+091} was detected with the ECLAIRs instrument on board the \textit{SVOM} mission. We present here a time-resolved spectroscopic analysis of the burst, along with the detection of burst oscillations within a 51-second interval during the decay phase. The oscillation frequency is measured to be $ν= 413.674 \pm 0.002\,\mathrm{Hz}$, consistent with previous reports. However, we detect a significant downward frequency drift over the burst duration, characterized by $\dotν = (-4.7 \pm 0.3) \times 10^{-3}\,\mathrm{Hz\,s^{-1}}$. This frequency evolution is atypical compared to those observed in similar burst oscillation sources. We tentatively attribute the observed drift to a Doppler shift induced by orbital motion. Under this interpretation, the inferred orbital period must be shorter than 20 minutes, placing \textit{4U~0614+091} among the most compact known low-mass X-ray binaries.

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arXiv2024

3U Transat: a cubesat constellation to boost the multi-messenger astronomy

Thanks to the advent of sensitive gravitational wave (GW) and neutrino detectors, multi-messenger (MM) astronomy will deeply transform our understanding of the Universe contents and evolution over cosmological times. To fully exploit the forthcoming GW and neutrino discoveries, it is crucial to detect as many electromagnetic (EM) counterparts as possible, but up to now, only one event has been detected by both GW detectors (Ligo/Virgo) and electromagnetic detectors (Fermi/GBM (Gamma ray Burst Monitor) and Integral), the short gamma-ray burst GRB 170817A/GW 170817 associated with the merger of a binary neutron star. To help improving the rate of joint MM events, it is crucial for the EM detectors in particular at high-energy in space to observe all the sky with a decent sensitivity. To do so, we propose the development of 3U Transat (TRANsient sky SATellites) project. 3U Transat is a constellation of nano-satellites offering a full sky coverage with a limited investment. The goal of this article is to present the 3U Transat project and its main scientific drivers as well as its current status. We will also describe our dynamic simulator used to optimise the scientific performances of the constellation. We will show highlights of the expected performances in term of detection and localisation capabilities as a function of the number of satellites in the constellation.

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arXiv2024

High-z gamma-ray burst detection by SVOM/ECLAIRs: Impact of instrumental biases on the bursts' measured properties

Context. Gamma-ray bursts (GRBs) can be detected at cosmological distances and therefore can be used to study the contents and phases of the early Universe. The 4-150 keV wide-field trigger camera ECLAIRs to fly on board the Space-based multi-band Variable Object Monitor (SVOM) mission, dedicated to studying the high-energy transient sky in synergy with multi-messenger follow-up instruments, has been adapted to detect high-redshift (high-z) GRBs. Aims. Investigating the detection capabilities of ECLAIRs for high-z GRBs and estimating the impacts of instrumental biases in reconstructing some of the source measured properties, focusing on GRB duration biases as a function of redshift. Methods. We simulated realistic detection scenarios for a sample of 162 already observed GRBs with known redshift values as they would have been seen by ECLAIRs. We simulated them at redshift values equal and higher than their measured value. Then, we assessed whether they would be detected with a trigger algorithm resembling that on board of ECLAIRs, and derived quantities such as T90, for those that would have been detected. Results. We find that ECLAIRs would be capable of detecting GRBs up to very high redshift values (e.g. 20 GRBs in our sample are detectable within more than 0.4 of the ECLAIRs field of view for z > 12). The ECLAIRs low-energy threshold of 4 keV, contributes to this great detection capability, as it may enhance it at high redshift (z > 10) by over 10% compared to a 15 keV low-energy threshold. We also show that the detection of GRBs at high-z values may imprint tip-of-the-iceberg biases on the GRB duration measurements, which can affect the reconstruction of other source properties.

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arXiv2024

Study of SVOM/ECLAIRs inhomogeneities in the detection plane below 8 keV and their mitigation for the trigger performances

The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a Chinese-French mission dedicated to the study of the transient sky. It is scheduled to start operations in 2024. ECLAIRs is a coded-mask telescope with a large field of view. It is designed to detect and localize gamma-ray bursts (GRBs) in the energy range from 4 keV up to 120 keV. In 2021, the ECLAIRs telescope underwent various calibration campaigns in vacuum test-chambers to evaluate its performance. Between 4 and 8 keV, the counting response of the detection plane shows inhomogeneities between pixels from different production batches. The efficiency inhomogeneity is caused by low-efficiency pixels (LEPs) from one of the two batches, together with high-threshold pixels (HTPs) whose threshold was raised to avoid cross-talk effects. In addition, some unexpected noise was found in the detection plane regions close to the heat pipes. We study the impact of these inhomogeneities and of the heat-pipe noise at low energies on the ECLAIRs onboard triggers. We propose different strategies in order to mitigate these impacts and to improve the onboard trigger performance. We analyzed the data from the calibration campaigns and performed simulations with the ground model of the ECLAIRs trigger software in order to design and evaluate the different strategies. Most of the impact of HTPs can be corrected for by excluding HTPs from the trigger processing. To correct for the impact of LEPs, an efficiency correction in the shadowgram seems to be a good solution. An effective solution for the heat-pipe noise is selecting the noisy pixels and ignoring their data in the 4--8 keV band during the data analysis.

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arXiv2020

Steady-state nucleosynthesis throughout the Galaxy

Measurement and astrophysical interpretation of characteristic gamma-ray lines from nucleosynthesis was one of the prominent science goals of the INTEGRAL mission and in particular its spectrometer SPI. Emission from 26Al and from 60Fe decay lines originates from accumulated ejecta of nucleosynthesis sources, and appears diffuse in nature. 26Al and 60Fe are believed to originate mostly from massive star clusters. Gamma-ray observations open an interesting window to trace the fate and flow of nucleosynthesis ejecta, after they have left the immediate sources and their birth sites, and on their path to mix with ambient interstellar gas. The INTEGRAL 26Al emission image confirms earlier findings of clumpiness and an extent along the entire plane of the Galaxy, supporting its origin from massive-star groups. INTEGRAL spectroscopy resolved the line and found Doppler broadenings and systematic shifts from large-scale galactic rotation. But an excess velocity of ~200 km/s suggests that 26Al decays preferentially within large superbubbles that extend in forward directions between spiral arms. The detection of 26Al line emission from nearby Orion and the Eridanus superbubble supports this interpretation. Positrons from beta+ decays of 26Al and other nucleosynthesis ejecta have been found to not explain the morphology of positron annihilation gamma-rays at 511 keV that have been measured by INTEGRAL. The 60Fe signal measured by INTEGRAL is diffuse but too weak for an imaging interpretation, an origin from point-like/concentrated sources is excluded. The 60Fe/26Al ratio is constrained to a range 0.2-0.4. Beyond improving precision of these results, diffuse nucleosynthesis contributions from novae (through 22Na radioactivity) and from past neutron star mergers in our Galaxy (from r-process radioactivity) are exciting new prospects for the remaining mission extensions.

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arXiv2019

Simulations of the SVOM/ECLAIRs Dynamic Background: A fast, accurate and general approach for wide-field hard X-ray instruments

The Space Variable Object Monitor (SVOM) is a forthcoming Chinese - French astrophysics space mission dedicated to the study of Gamma-ray bursts and high-energy transients. ECLAIRs, a wide-field hard X-ray coded mask imager, is the leading instrument for the transient detection and their first localisation. The sensitivity of such instruments is usually limited by the background, either of instrumental or astrophysical origin. Detailed estimations of the background are obtained by simulating the interaction of particles with the matter using, in the present case, the GEANT4 Monte-Carlo toolkit. However, this is a time consuming process, especially when it is needed to carry out all possible geometrical and orbital configurations. Instead, we present a much faster method that allows computing the background in either a static or dynamic (time dependent) way. The method is based on the preliminary calculation of a large particle database using the GEANT4 toolkit followed by a selection process based on the incoming direction and energy of the particles. This approach is as accurate as direct Monte-Carlo methods, while it reduces the computation time by a factor of $10^3 - 10^4$ for our application. We apply this method to compute the SVOM/ECLAIRs dynamic background.

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arXiv2015

The Galactic $^{26}$Al emission map as revealed by INTEGRAL/SPI

Diffuse emission is often challenging since it is undetectable by most instruments, which are generally dedicated to point-source studies. The $^{26}$Al emission is a good illustration: the only available $^{26}$Al map to date has been released, more than fifteen years ago, thanks to the COMPTEL instrument. However, at the present time, the SPI spectrometer aboard the INTEGRAL mission offers a unique opportunity to enrich this first result. In this paper, 2 $\times$ 10$^8$ s of data accumulated between 2003 and 2013 are used to perform a dedicated analysis, aiming to deeply investigate the spatial morphology of the $^{26}$Al emission. The data are first compared with several sky maps based on observations at various wavelengths to model the $^{26}$Al distribution throughout the Galaxy. For most of the distribution models, the inner Galaxy flux is compatible with a value of 3.3$\times$ 10$^{-4}$ ph.cm$^{-2}$.s$^{-1}$ while the preferred template maps correspond to young stellar components such as core-collapse supernovae, Wolf-Rayet and massive AGB stars. To get more details about this emission, an image reconstruction is performed using an algorithm based on the maximum-entropy method. In addition to the inner Galaxy emission, several excesses suggest that some sites of emission are linked to the spiral arms structure. Lastly, an estimation of the $^{60}$Fe line flux, assuming a spatial distribution similar to $^{26}$Al line emission, results in a $^{60}$Fe\ to $^{26}$Al ratio around 0.14, which agrees with the most recent studies and with the SN explosion model predictions.

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arXiv2012

The magnetic field in the X-ray corona of Cygnus X-1

The different electron distributions in the hard and soft spectral states (HS and SS) of BH binaries could be caused by kinetic processes and changing because of varying physical conditions in the corona. In presence of a magnetic field in the corona, the electron distribution can appear thermal, even when acceleration mechanisms would produce non thermal distributions. This is due to fast and efficient thermalization through synchrotron self-absorption. We have analyzed data from 6 years of observations of Cygnus X-1 with the INTEGRAL observatory and produced 12 high-quality, stacked broad-band hard X-ray spectra representative of the whole range of spectral shapes observed. We then fit these spectra with hybrid thermal/non-thermal Comptonization models and study the evolution of the physical parameters of the accretion flow across the spectral transition. In particular, we use the BELM model to constrain the magnetic field in the corona through its effects on the coronal emission. Indeed, the hot electrons of the X-ray corona produce soft (optical-UV) synchrotron radiation which is then Comptonized and may affect the temperature of the electrons through Compton cooling. We find that in the SS, the emission is dominated by Comptonization of the disc photons and the magnetic field is at most of the order of 1E+06 G. In the hard states, the data are consistent with a pure synchrotron self-Compton model. If the non-thermal excess observed above a few hundred keV in the HS is produced in the same region as the bulk of the thermal Comptonization, we obtain an upper limit on the coronal magnetic field of about 1E+05 G. If, on the other hand, the non-thermal excess is produced in a different location, the constraints on the magnetic field in the HS are somewhat relaxed and the upper limit rises to 1E+07 G. We discuss these constraints in the context of current accretion flow models.

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arXiv2011

Extended hard X-ray emission from the Vela pulsar wind nebula

The nebula powered by the Vela pulsar is one of the best examples of an evolved pulsar wind nebula, allowing to access the particle injection history and the interaction with the supernova ejecta. We report on the INTEGRAL discovery of extended emission above 18 keV from the Vela nebula. The northern side has no known counterparts and it appears larger and more significant than the southern one, which is in turn partially coincident with the cocoon, the soft X-ray and TeV filament towards the center of the remnant. We also present the spectrum of the Vela nebula in the 18-400 keV energy range as measured by IBIS/ISGRI and SPI on board the INTEGRAL satellite. The apparent discrepancy between IBIS/ISGRI, SPI, and previous measurements is understood in terms of point spread function, supporting the hypothesis of a nebula more diffuse than previously thought. A break at ~25 keV is found in the spectrum within 6' from the pulsar after including the Suzaku XIS data. Interpreted as a cooling break, this points out that the inner nebula is composed by electrons injected in the last ~2000 years. Broad-band modeling also implies a magnetic field higher than 10 microGauss in this region. Finally, we discuss the nature of the northern emission, which might be due to fresh particles injected after the passage of the reverse shock.

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arXiv2011

Diffuse emission measurement with INTEGRAL/SPI as indirect probe of cosmic-ray electrons and positrons

Significant advances have been made in the understanding of the diffuse Galactic hard X-ray continuum emission using data from the INTEGRAL observatory. The diffuse hard power-law component seen with the INTEGRAL/SPI spectrometer has been identified with inverse-Compton emission from relativistic (GeV) electrons on the cosmic microwave background and Galactic interstellar radiation field. In the present analysis, SPI data from 2003 to 2009, with a total exposure time of ~ 10^8 s, are used to derive the Galactic ridge hard X-ray spatial distribution and spectrum between 20 keV and 2.4 MeV. Both are consistent with predictions from the GALPROP code. The good agreement between measured and predicted emission from keV to GeV energies suggests that the correct production mechanisms have been identified. We discuss the potential of the SPI data to provide an indirect probe of the interstellar cosmic-ray electron distribution, in particular for energies below a few GeV.

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arXiv2010

On the morphology of the electron-positron annihilation emission as seen by SPI/INTEGRAL

The 511 keV positron annihilation emission remains a mysterious component of the high energy emission of our Galaxy. Its study was one of the key scientific objective of the SPI spectrometer on-board the INTEGRAL satellite. In fact, a lot of observing time has been dedicated to the Galactic disk with a particular emphasis on the central region. A crucial issue in such an analysis concerns the reduction technique used to treat this huge quantity of data, and more particularly the background modeling. Our method, after validation through a variety of tests, is based on detector pattern determination per ~6 month periods, together with a normalisation variable on a few hour timescale. The Galactic bulge is detected at a level of ~70 sigma allowing more detailed investigations. The main result is that the bulge morphology can be modelled with two axisymmetric Gaussians of 3.2 deg. and 11.8 deg. FWHM and respective fluxes of 2.5 and 5.4 x 10^-4 photons/(cm^2.s^1). We found a possible shift of the bulge centre towards negative longitude at l=-0.6 +/- 0.2 degrees. In addition to the bulge, a more extended structure is detected significantly with flux ranging from 1.7 to 2.9 x10^-3 photons/(cm^2.s^1) depending on its assumed geometry (pure disk or disk plus halo). The disk emission is also found to be symmetric within the limits of the statistical errors.

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arXiv2008

Inverse Compton Origin of the Hard X-Ray and Soft Gamma-Ray Emission from the Galactic Ridge

A recent re-determination of the non-thermal component of the hard X-ray to soft gamma-ray emission from the Galactic ridge, using the SPI instrument on the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) Observatory, is shown to be well reproduced as inverse-Compton emission from the interstellar medium. Both cosmic-ray primary electrons and secondary electrons and positrons contribute to the emission. The prediction uses the GALPROP model and includes a new calculation of the interstellar radiation field. This may solve a long-standing mystery of the origin of this emission, and potentially opens a new window on Galactic cosmic rays.

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arXiv2004

INTEGRAL, XMM-Newton and Rossi-XTE Observations of the State Transition of the X-ray Transient and Black Hole Candidate XTE J1720-318

We report the results of extensive high-energy observations of the X-ray transient and black hole candidate XTE J1720-318 performed with INTEGRAL, XMM-Newton and RXTE. The source, which underwent an outburst in January 2003, was observed in February in a spectral state dominated by a soft component with a weak high-energy tail. The XMM-Newton data provided a high column density Nh of 1.2*e22 cm^{-2} which suggests that the source lies at the Galactic Center distance. The simultaneous RXTE and INTEGRAL Target of Opportunity observations allowed us to measure the weak and steep tail, typical of a black-hole binary in the so-called High/Soft State. We could follow the evolution of the source outburst over several months using the INTEGRAL Galactic Center survey observations. The source regained activity at the end of March: it showed a clear transition towards a much harder state, and then decayed to a quiescent state in summer. In the hard state, the source was detected up to 200 keV with a typical power law index of 1.8 and a peak luminosity of 7.5*e36 ergs s^{-1} in the 2-100 keV band, for an assumed distance of 8 kpc. We conclude that XTE J1720-318 is indeed representative of the class of the black hole X-ray novae which populate our Galactic bulge and we discuss its properties in the frame of the spectral models used for transient black hole binaries.

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arXiv2004

Contribution of point sources to the soft gamma-ray Galactic emission

The nature of the soft gamma-ray (20-200 keV) Galactic emission has been a matter of debate for a long time. Previous experiments have tried to separate the point source contribution from the real interstellar emission, but with a rather poor spatial resolution, they concluded that the interstellar emission could be a large fraction of the total Galactic emission. INTEGRAL, having both high resolution and high sensitivity, is well suited to reassess more precisely this problem. Using the INTEGRAL core program Galactic Center Deep Exposure (GCDE), we estimate the contribution of detected point sources to the total Galactic flux.

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