Sylvain Chaty | Université Paris Diderot (original) (raw)

Papers by Sylvain Chaty

Monthly Notices of the Royal Astronomical Society, 2003

We report multiwavelength observations of the soft X-ray transient XTE J1118+480, which we observ... more We report multiwavelength observations of the soft X-ray transient XTE J1118+480, which we observed with UKIRT, Hubble Space Telescope (HST), RXTE, Extreme Ultraviolet Explorer (EUVE) and many other instruments and facilities. Adding radio (Ryle Telescope, VLA), submillimetre (JCMT) and X-ray (Chandra and SAX) data from the literature, we assembled the most complete spectral energy distribution (SED) of this source yet published. We followed the evolution of this source for 1 yr, including six observations performed during the outburst, and one observation at the end of the outburst. Because of the unusually high galactic latitude of XTE J1118+480, it suffers from very low extinction, and its SED is nearly complete, including extreme ultraviolet observations. XTE J1118+480 exhibits an unusually low low/hard state (estimated inner radius of 350R s ) and a strong non-thermal contribution in the radio to optical domain, which is likely to be due to synchrotron emission. We discuss the interstellar column density and show that it is low, between 0.80 and 1.30×10 20 cm −2 . We analyse the evolution of the SED during the outburst, including the contributions from the companion star, the accretion disc, the outflow, and relating irradiation and variability of the source in different bands to the SED. We find no significant spectral variability during the outburst evolution, consistent with the presence of a steady outflow. An analysis of its outflow to accretion energy ratio suggests that the microquasar XTE J1118+480 is analogous to radio-quiet quasars. This, combined with the inverted spectrum from radio to optical, makes XTE J1118+480 very similar to other microquasar sources, e.g. GRS 1915+105 and GX 339−4 in their low/hard state. We model the high-energy emission with a hot disc model, and discuss different accretion models for the broad-band spectrum of XTE J1118+480.

We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7-... more We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7-11 2003. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an intermediate state. As expected during state transitions, we find an anticorrelation between the 3-10 keV and the 15 GHz radio fluxes and a strong correlation between the 3-200 keV hardness and radio flux.

We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7-... more We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7- 11 2003. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an inter- mediate state. As expected during state transitions, we find an anticorrelation between the 3-10 keV and the 15 GHz radio fluxes and a strong correlation be- tween the 3-200 keV hardness and radio flux. Key words: Gamma-rays; X-ray binaries; black holes; Individual: Cyg X-1.

Astronomy and Astrophysics, 2006

We report the results of an observation of Cygnus X-1 performed on June 7-11 2003 with INTEGRAL t... more We report the results of an observation of Cygnus X-1 performed on June 7-11 2003 with INTEGRAL that we combine with simultaneous radio observations with the Ryle telescope. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an Intermediate State. The INTEGRAL spectrum shows a high-energy cut-off or break around 100 keV. The shape of this cut-off differs from pure thermal Comptonisation, suggesting the presence of a non-thermal component at higher energies. The average broad band spectrum is well represented by hybrid thermal/non-thermal Comptonisation models. However, models with mono-energetic injection, or models with an additional soft component are favoured over standard power-law acceleration models. During the 4 day long observation the broad band (3-200 keV) luminosity varied by up to a factor of 2.6 and the source showed an important spectral variability. A principal component analysis demonstrates that most of this variability occurs through 2 independent modes. The first mode consists in changes in the overall luminosity on time scale of hours with almost constant spectra (responsible for 68 % of the variance) that are strikingly uncorrelated with the variable radio flux. We interpret this variability mode as variations of the dissipation rate in the corona, possibly associated with magnetic flares. The second variability mode consists in a pivoting of the spectrum around ∼10 keV (27 % of the variance). It acts on a longer time-scale: initially soft, the spectrum hardens in the first part of the observation and then softens again. This pivoting pattern is strongly correlated with the radio (15 GHz) emission: radio fluxes are stronger when the INTEGRAL spectrum is harder We propose that the pivoting mode represents a 'mini' state transition from a nearly High Soft State to a nearly Low Hard State , and back. This mini-transition would be caused by changes in the soft cooling photons flux in the hot Comptonising plasma associated with an increase of the temperature of the accretion disc. The jet power then appears to be anti-correlated with the disc luminosity and unrelated to the coronal power. This is in sharp contrast with previous results obtained for the Low Hard State, suggesting a different mode of coupling between the jet, the cold disc, and the corona in Intermediate States. From this interpretation we also infer that the bolometric luminosity jumps by a factor of about 2 during the transition hard to soft, suggesting a radiatively inefficient accretion flow in the Low Hard State.

La polarización de la luz de binarias de rayos X no ha sido muy estudiada. Sin embargo, puede dar... more La polarización de la luz de binarias de rayos X no ha sido muy estudiada. Sin embargo, puede dar mucha información sobre la geometría de la fuente así como de la extensión posible de emisión de chorros relativistas hacia las longitudes de ondaópticas. Presentamos aquí un programa preliminar para buscar estas características observacionales.

CHATY Sylvain ; Né le : 16/10/1971 à Maisons-Alfort (94) ; Nationalité : française AIM Astrophysi... more CHATY Sylvain ; Né le : 16/10/1971 à Maisons-Alfort (94) ; Nationalité : française AIM Astrophysique Interactions Multi-echelles (

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (fo... more The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST, launched June 11, 2008), has observed a weekly-averaged continuous and increasing trend in the gamma-ray flux from the blazar 3C 279 (J2000, R.A. :12h56m11.1665s, Dec:-05d47m21.523s) for the last six weeks. Preliminary analysis indicates that the source is continuing this high state with a gamma-ray flux (E>100MeV) now in excess of 1.5 x 10-6 photons cm-2 s-1.

We have an accepted Chandra/Swift ToO proposal for observation of one new bright Galactic transie... more We have an accepted Chandra/Swift ToO proposal for observation of one new bright Galactic transient detected by the GLAST Large Area Telescope (LAT) at |b| < 5 with a flux exceeding 2 10-6 cm-2 s-1 above 100 MeV. The goal of this proposal is to determine the nature of an event similar to the intense, non-blazar, transient of presumably Galactic

We have an accepted Chandra/Swift ToO proposal for observation of one new bright Galactic transie... more We have an accepted Chandra/Swift ToO proposal for observation of one new bright Galactic transient detected by the FERMI Large Area Telescope (LAT) at |b| < 5 with a flux exceeding 2 10-6 cm-2 s-1 above 100 MeV. The goal of this proposal is to determine the nature of an event similar to the intense, non-blazar, transient of presumably Galactic

A new type of high-energy binary system has been revealed by the INTEGRAL satellite. These source... more A new type of high-energy binary system has been revealed by the INTEGRAL satellite. These sources are being unveiled by means of multi-wavelength optical, near- and midinfrared observations. Among these sources, two distinct classes are appearing: the first one is constituted of intrinsically obscured high-energy sources, of which IGR J16318-4848 seems to be the most extreme example. The second one

AIP Conference Proceedings, 2007

A new type of high-energy binary systems has been revealed by the INTEGRAL satellite. These sourc... more A new type of high-energy binary systems has been revealed by the INTEGRAL satellite. These sources are in the course of being unveiled by means of multi-wavelength optical, near-and mid-infrared observations. Among these sources, two distinct classes are appearing: the first one is constituted of intrinsically obscured high-energy sources, of which IGR J16318-4848 seems to be the most extreme example. The second one is populated by the so-called supergiant fast X-ray transients, with IGR J17544-2619 being the archetype. We report here on multi-wavelength optical to mid-infrared observations of these systems. We show that in the case of the obscured sources our observations suggest the presence of absorbing material (dust and/or cold gas) enshrouding the whole binary system. We then discuss the nature of these two different types of systems.

AIP Conference Proceedings, 2008

We report on Ihe observation of two quiescent stage Soft X-my transients -the BH-SXT 081124-68 an... more We report on Ihe observation of two quiescent stage Soft X-my transients -the BH-SXT 081124-68 and the NS-SXT J2123-058.

The Astrophysical Journal Supplement Series, 2008

We describe a uniform all-sky survey of bright blazars, selected primarily by their flat radio sp... more We describe a uniform all-sky survey of bright blazars, selected primarily by their flat radio spectra, that is designed to provide a large catalog of likely -ray active galactic nuclei (AGNs). The defined sample has 1625 targets with radio and X-ray properties similar to those of the EGRET blazars, spread uniformly across the jbj > 10 sky. We also report progress toward optical characterization of the sample; of objects with known R < 23, 85% have been classified and 81% have measured redshifts. One goal of this program is to focus attention on the most interesting (e.g., high-redshift, high-luminosity, . . .) sources for intensive multiwavelength study during the observations by the Large Area Telescope (LAT) on GLAST.

Abstract This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Larg... more Abstract This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for ...

The INTEGRAL satellite has revealed a major population of Supergiant X-ray Binaries in our Galaxy... more The INTEGRAL satellite has revealed a major population of Supergiant X-ray Binaries in our Galaxy, revolutionizing our understanding of high-mass binary systems and their evolution. This population, constituted of a compact object orbiting around a massive and luminous supergiant star, exhibits unusual properties, either being extremely absorbed, or showing very short and intense flares. An intensive set of multi-wavelength observations has led us to reveal their nature, and to show that these systems are wind-fed accretors, closely related to massive star forming regions. In this paper I describe the characteristics of these sources, showing that this newly revealed population is linked to the evolution of gamma-ray emitting massive stars with a compact companion.

Advances in Space Research, 2013

ABSTRACT In this review I first describe the nature of the three kinds of High-Mass X-ray Binarie... more ABSTRACT In this review I first describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: (i) Be circumstellar disc, (ii) supergiant stellar wind, and (iii) Roche lobe filling supergiants. I then report on the discovery of two new populations of HMXBs hosting supergiant stars, recently revealed by a wealth of new observations, coming from the high energy side (INTEGRAL, Swift, XMM, Chandra satellites), and complemented by multi-wavelength optical/infrared observations (mainly ESO facilities). The first population is constituted of obscured supergiant HMXBs, the second one of supergiant fast X-ray transients (SFXTs), exhibiting short and intense X-ray flares. I finally discuss the formation and evolution of HMXBs, constrain the accretion models (e.g. clumpy winds, transitory accretion disc, magneto-centrifugal barrier), show evidences suggesting the existence of an evolutionary link, include comparisons with population synthesis models, and finally build a consistent scenario explaining the various characteristics of these extreme celestial sources. Because they are the likely progenitors of Luminous Blue Variables (LBVs), and also of neutron star/black hole binary mergers, related to short/hard gamma-ray bursts, the knowledge of the nature, formation and evolution of these HMXB populations is of prime importance.

Monthly Notices of the Royal Astronomical Society, 2003

We report multiwavelength observations of the soft X-ray transient XTE J1118+480, which we observ... more We report multiwavelength observations of the soft X-ray transient XTE J1118+480, which we observed with UKIRT, Hubble Space Telescope (HST), RXTE, Extreme Ultraviolet Explorer (EUVE) and many other instruments and facilities. Adding radio (Ryle Telescope, VLA), submillimetre (JCMT) and X-ray (Chandra and SAX) data from the literature, we assembled the most complete spectral energy distribution (SED) of this source yet published. We followed the evolution of this source for 1 yr, including six observations performed during the outburst, and one observation at the end of the outburst. Because of the unusually high galactic latitude of XTE J1118+480, it suffers from very low extinction, and its SED is nearly complete, including extreme ultraviolet observations. XTE J1118+480 exhibits an unusually low low/hard state (estimated inner radius of 350R s ) and a strong non-thermal contribution in the radio to optical domain, which is likely to be due to synchrotron emission. We discuss the interstellar column density and show that it is low, between 0.80 and 1.30×10 20 cm −2 . We analyse the evolution of the SED during the outburst, including the contributions from the companion star, the accretion disc, the outflow, and relating irradiation and variability of the source in different bands to the SED. We find no significant spectral variability during the outburst evolution, consistent with the presence of a steady outflow. An analysis of its outflow to accretion energy ratio suggests that the microquasar XTE J1118+480 is analogous to radio-quiet quasars. This, combined with the inverted spectrum from radio to optical, makes XTE J1118+480 very similar to other microquasar sources, e.g. GRS 1915+105 and GX 339−4 in their low/hard state. We model the high-energy emission with a hot disc model, and discuss different accretion models for the broad-band spectrum of XTE J1118+480.

We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7-... more We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7-11 2003. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an intermediate state. As expected during state transitions, we find an anticorrelation between the 3-10 keV and the 15 GHz radio fluxes and a strong correlation between the 3-200 keV hardness and radio flux.

We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7-... more We present preliminary results of an observation of Cygnus X-1 with INTEGRAL performed on June 7- 11 2003. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an inter- mediate state. As expected during state transitions, we find an anticorrelation between the 3-10 keV and the 15 GHz radio fluxes and a strong correlation be- tween the 3-200 keV hardness and radio flux. Key words: Gamma-rays; X-ray binaries; black holes; Individual: Cyg X-1.

Astronomy and Astrophysics, 2006

We report the results of an observation of Cygnus X-1 performed on June 7-11 2003 with INTEGRAL t... more We report the results of an observation of Cygnus X-1 performed on June 7-11 2003 with INTEGRAL that we combine with simultaneous radio observations with the Ryle telescope. Both spectral and variability properties of the source indicate that Cygnus X-1 was in an Intermediate State. The INTEGRAL spectrum shows a high-energy cut-off or break around 100 keV. The shape of this cut-off differs from pure thermal Comptonisation, suggesting the presence of a non-thermal component at higher energies. The average broad band spectrum is well represented by hybrid thermal/non-thermal Comptonisation models. However, models with mono-energetic injection, or models with an additional soft component are favoured over standard power-law acceleration models. During the 4 day long observation the broad band (3-200 keV) luminosity varied by up to a factor of 2.6 and the source showed an important spectral variability. A principal component analysis demonstrates that most of this variability occurs through 2 independent modes. The first mode consists in changes in the overall luminosity on time scale of hours with almost constant spectra (responsible for 68 % of the variance) that are strikingly uncorrelated with the variable radio flux. We interpret this variability mode as variations of the dissipation rate in the corona, possibly associated with magnetic flares. The second variability mode consists in a pivoting of the spectrum around ∼10 keV (27 % of the variance). It acts on a longer time-scale: initially soft, the spectrum hardens in the first part of the observation and then softens again. This pivoting pattern is strongly correlated with the radio (15 GHz) emission: radio fluxes are stronger when the INTEGRAL spectrum is harder We propose that the pivoting mode represents a 'mini' state transition from a nearly High Soft State to a nearly Low Hard State , and back. This mini-transition would be caused by changes in the soft cooling photons flux in the hot Comptonising plasma associated with an increase of the temperature of the accretion disc. The jet power then appears to be anti-correlated with the disc luminosity and unrelated to the coronal power. This is in sharp contrast with previous results obtained for the Low Hard State, suggesting a different mode of coupling between the jet, the cold disc, and the corona in Intermediate States. From this interpretation we also infer that the bolometric luminosity jumps by a factor of about 2 during the transition hard to soft, suggesting a radiatively inefficient accretion flow in the Low Hard State.

La polarización de la luz de binarias de rayos X no ha sido muy estudiada. Sin embargo, puede dar... more La polarización de la luz de binarias de rayos X no ha sido muy estudiada. Sin embargo, puede dar mucha información sobre la geometría de la fuente así como de la extensión posible de emisión de chorros relativistas hacia las longitudes de ondaópticas. Presentamos aquí un programa preliminar para buscar estas características observacionales.

CHATY Sylvain ; Né le : 16/10/1971 à Maisons-Alfort (94) ; Nationalité : française AIM Astrophysi... more CHATY Sylvain ; Né le : 16/10/1971 à Maisons-Alfort (94) ; Nationalité : française AIM Astrophysique Interactions Multi-echelles (

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (fo... more The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST, launched June 11, 2008), has observed a weekly-averaged continuous and increasing trend in the gamma-ray flux from the blazar 3C 279 (J2000, R.A. :12h56m11.1665s, Dec:-05d47m21.523s) for the last six weeks. Preliminary analysis indicates that the source is continuing this high state with a gamma-ray flux (E>100MeV) now in excess of 1.5 x 10-6 photons cm-2 s-1.

We have an accepted Chandra/Swift ToO proposal for observation of one new bright Galactic transie... more We have an accepted Chandra/Swift ToO proposal for observation of one new bright Galactic transient detected by the GLAST Large Area Telescope (LAT) at |b| < 5 with a flux exceeding 2 10-6 cm-2 s-1 above 100 MeV. The goal of this proposal is to determine the nature of an event similar to the intense, non-blazar, transient of presumably Galactic

We have an accepted Chandra/Swift ToO proposal for observation of one new bright Galactic transie... more We have an accepted Chandra/Swift ToO proposal for observation of one new bright Galactic transient detected by the FERMI Large Area Telescope (LAT) at |b| < 5 with a flux exceeding 2 10-6 cm-2 s-1 above 100 MeV. The goal of this proposal is to determine the nature of an event similar to the intense, non-blazar, transient of presumably Galactic

A new type of high-energy binary system has been revealed by the INTEGRAL satellite. These source... more A new type of high-energy binary system has been revealed by the INTEGRAL satellite. These sources are being unveiled by means of multi-wavelength optical, near- and midinfrared observations. Among these sources, two distinct classes are appearing: the first one is constituted of intrinsically obscured high-energy sources, of which IGR J16318-4848 seems to be the most extreme example. The second one

AIP Conference Proceedings, 2007

A new type of high-energy binary systems has been revealed by the INTEGRAL satellite. These sourc... more A new type of high-energy binary systems has been revealed by the INTEGRAL satellite. These sources are in the course of being unveiled by means of multi-wavelength optical, near-and mid-infrared observations. Among these sources, two distinct classes are appearing: the first one is constituted of intrinsically obscured high-energy sources, of which IGR J16318-4848 seems to be the most extreme example. The second one is populated by the so-called supergiant fast X-ray transients, with IGR J17544-2619 being the archetype. We report here on multi-wavelength optical to mid-infrared observations of these systems. We show that in the case of the obscured sources our observations suggest the presence of absorbing material (dust and/or cold gas) enshrouding the whole binary system. We then discuss the nature of these two different types of systems.

AIP Conference Proceedings, 2008

We report on Ihe observation of two quiescent stage Soft X-my transients -the BH-SXT 081124-68 an... more We report on Ihe observation of two quiescent stage Soft X-my transients -the BH-SXT 081124-68 and the NS-SXT J2123-058.

The Astrophysical Journal Supplement Series, 2008

We describe a uniform all-sky survey of bright blazars, selected primarily by their flat radio sp... more We describe a uniform all-sky survey of bright blazars, selected primarily by their flat radio spectra, that is designed to provide a large catalog of likely -ray active galactic nuclei (AGNs). The defined sample has 1625 targets with radio and X-ray properties similar to those of the EGRET blazars, spread uniformly across the jbj > 10 sky. We also report progress toward optical characterization of the sample; of objects with known R < 23, 85% have been classified and 81% have measured redshifts. One goal of this program is to focus attention on the most interesting (e.g., high-redshift, high-luminosity, . . .) sources for intensive multiwavelength study during the observations by the Large Area Telescope (LAT) on GLAST.

Abstract This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Larg... more Abstract This NAPA proposal will be triggered by the detection of a gamma-ray flare with the Large Area Telescope on the Fermi gamma-ray satellite. The Fermi team will identify bright sources flaring on day-timescales to trigger ATCA observations for southern sources for ...

The INTEGRAL satellite has revealed a major population of Supergiant X-ray Binaries in our Galaxy... more The INTEGRAL satellite has revealed a major population of Supergiant X-ray Binaries in our Galaxy, revolutionizing our understanding of high-mass binary systems and their evolution. This population, constituted of a compact object orbiting around a massive and luminous supergiant star, exhibits unusual properties, either being extremely absorbed, or showing very short and intense flares. An intensive set of multi-wavelength observations has led us to reveal their nature, and to show that these systems are wind-fed accretors, closely related to massive star forming regions. In this paper I describe the characteristics of these sources, showing that this newly revealed population is linked to the evolution of gamma-ray emitting massive stars with a compact companion.

Advances in Space Research, 2013

ABSTRACT In this review I first describe the nature of the three kinds of High-Mass X-ray Binarie... more ABSTRACT In this review I first describe the nature of the three kinds of High-Mass X-ray Binaries (HMXBs), accreting through: (i) Be circumstellar disc, (ii) supergiant stellar wind, and (iii) Roche lobe filling supergiants. I then report on the discovery of two new populations of HMXBs hosting supergiant stars, recently revealed by a wealth of new observations, coming from the high energy side (INTEGRAL, Swift, XMM, Chandra satellites), and complemented by multi-wavelength optical/infrared observations (mainly ESO facilities). The first population is constituted of obscured supergiant HMXBs, the second one of supergiant fast X-ray transients (SFXTs), exhibiting short and intense X-ray flares. I finally discuss the formation and evolution of HMXBs, constrain the accretion models (e.g. clumpy winds, transitory accretion disc, magneto-centrifugal barrier), show evidences suggesting the existence of an evolutionary link, include comparisons with population synthesis models, and finally build a consistent scenario explaining the various characteristics of these extreme celestial sources. Because they are the likely progenitors of Luminous Blue Variables (LBVs), and also of neutron star/black hole binary mergers, related to short/hard gamma-ray bursts, the knowledge of the nature, formation and evolution of these HMXB populations is of prime importance.