arXiv subjects

Stephane Corbel

Publications and source records attributed to Stephane Corbel.

46 records · Page 3Linked to original sources

arXiv2004

Orbital Parameters for the Black Hole Binary XTE J1650-500

(Shortened) We present R-band photometry of the X-ray transient and candidate black hole binary XTE J1650-500 obtained between 2003 May and August with the 6.5m Clay Telescope. A timing analysis of these data reveals a photometric period of 0.3205 +/- 0.0007 days (i.e. 7.63 hr) with a possible alias at 0.3785 days (9.12 hr). Our photometry completely rules out the previously published spectroscopic period of 0.212 days (5.09 hr). Consequently, we reanalyzed the 15 archival ESO/VLT spectra (obtained 2002 June by Sanchez-Fernandez et al.) that were the basis of the previously published spectroscopic period. We used a ``restframe search'' technique that is well suited for cases when the signal-to-noise ratio of individual spectra is low. The results confirmed the photometric period of 0.3205 days, and rule out the alias period near 0.38 days. The best value for the velocity semiamplitude of the companion star is K_2 = 435 +/- 30 km/sec, and the corresponding optical mass function is f(M) = 2.73 +/- 0.56 solar masses. The amplitude of the phased R-band light curve is 0.2 magnitudes, which gives a lower limit to the inclination of 50 +/- 3 degrees in the limiting case of no contribution to the R-band light curve from the accretion disk. If the mass ratio of XTE J1650-500 is similar to the mass ratios of other black hole binaries like A0620-00 or GRS 1124-683 (e.g. Q >~ 10), then our lower limit to the inclination gives an upper limit to the mass of the black hole in XTE J1650-500 of M_1 <~ 7.3 solar masses. However, the mass can be considerably lower if the R-band flux is dominated by the accretion disk. For example, if the accretion disk does contribute 80% of the flux, as our preliminary results suggest, then the black hole mass would be only about 4 solar masses.

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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

An INTEGRAL Observation of the Black Hole Transient 4U 1630--47 and the Norma Region of the Galaxy

We report on results from a 2003 February INTEGRAL observation of the black hole candidate (BHC) 4U 1630-47 and the high energy sources in the Norma Region of the Galaxy and on RXTE and radio observations of 4U 1630-47. To date, there have been 38 new or previously poorly studied sources found by INTEGRAL (the ``IGR'' sources), and 15 of the IGR sources are in the field of view of our observation. We detect 12 of the 15 sources, and we speculate that a subset of the IGR sources may be part of a new population of persistent, hard, intermediate luminosity X-ray sources. During our observations, 4U 1630-47 was in an intermediate state with strong soft and hard components, a power-law photon index of 2.11-2.18, a 4% rms level of timing noise (0.1-10 Hz), and the source was not detected in the radio band. We discuss the evolution of the energy spectrum during the 293 ks INTEGRAL observation, and we report on rapid, high amplitude flaring behavior that has been seen for much of the 2002-2004 outburst.

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arXiv2003

A transient large-scale relativistic radio jet from GX 339-4

We report on the formation and evolution of a large-scale, synchrotron-emitting jet from the black hole candidate and X-ray binary system GX 339-4. In 2002 May, the source moved from a low/hard to a very high X-ray state, contemporaneously exhibiting a very bright optically thin radio flare. Further observations with the Australia Telescope Compact Array have tracked the formation of a collimated structure extending to about 12 arcsec, with apparent velocity greater than 0.9c. The luminosity of the outflow seems to be rapidly decreasing; these observations confirm that transient large-scale jets are likely to be common events triggered by X-ray state transitions in black hole X-ray binaries.

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arXiv2003

Chandra Detections of Two Quiescent Black Hole X-Ray Transients

Using the Chandra X-ray Observatory, we have detected the black hole transients V4641 Sgr and XTE J1859+226 in their low luminosity, quiescent states. The 0.3-8 keV luminosities are (4.0^(+3.3)_(-2.4))E31 (d/7 kpc)^2 erg/s and (4.2^(+4.8)_(-2.2))E31 (d/11 kpc)^2 erg/s for V4641 Sgr and XTE J1859+226, respectively. With the addition of these 2 systems, 14 out of the 15 transients with confirmed black holes (via compact object mass measurements) now have measured quiescent luminosities or sensitive upper limits. The only exception is GRS 1915+105, which has not been in quiescence since its discovery in 1992. The luminosities for V4641 Sgr and XTE J1859+226 are consistent with the median luminosity of 2E31 erg/s for the systems with previous detections. Our analysis suggests that the quiescent X-ray spectrum of V4641 Sgr is harder than for the other systems in this group, but, due to the low statistical quality of the spectrum, it is not clear if V4641 Sgr is intrinsically hard or if the column density is higher than the interstellar value. Focusing on V4641 Sgr, we compare our results to theoretical models for X-ray emission from black holes in quiescence. Also, we obtain precise X-ray positions for V4641 Sgr and XTE J1859+226 via cross-correlation of the X-ray sources detected near our targets with IR sources in the 2 Micron All-Sky Survey catalog.

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arXiv2003

X-Ray Flares and Oscillations from the Black Hole Candidate X-Ray Transient XTE J1650-500 at Low Luminosity

We report on X-ray observations made with the Rossi X-ray Timing Explorer of the black hole candidate (BHC) transient XTE J1650-500 at the end of its first, and currently only, outburst. By monitoring the source at low luminosities over several months, we found 6 bright ~100 second X-ray flares and long time scale oscillations of the X-ray flux. The oscillations are aperiodic with a characteristic time scale of 14.2 days and an order of magnitude variation in the 2.8-20 keV flux. The oscillations may be related to optical "mini-outbursts" that have been observed at the ends of outbursts for other short orbital period BHC transients. The X-ray flares have durations between 62 and 215 seconds and peak fluxes that are 5-24 times higher than the persistent flux. The flares have non-thermal energy spectra and occur when the persistent luminosity is near 3E34 (d/4 kpc)^2 erg/s (2.8-20 keV). The rise time for the brightest flare demonstrates that physical models for BHC systems must be able to account for the situation where the X-ray flux increases by a factor of up to 24 on a time scale of seconds. We discuss the flares in the context of observations and theory of Galactic BHCs and compare the flares to those detected from Sgr A*, the super-massive black hole at the Galactic center. We also compare the flares to X-ray bursts that are seen in neutron star systems. While some of the flare light curves are similar to those of neutron star bursts, the flares have non-thermal energy spectra in contrast to the blackbody spectra exhibited in bursts. This indicates that X-ray bursts should not be taken as evidence that a given system contains a neutron star unless the presence of a blackbody component in the burst spectrum can be demonstrated.

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arXiv2003

Radio Emission from an Ultraluminous X-Ray Source

The physical nature of ultraluminous x-ray sources is uncertain. Stellar mass black holes with beamed radiation and intermediate mass black holes with isotropic radiation are two plausible explanations. We discovered radio emission from an ultraluminous x-ray source in the dwarf irregular galaxy NGC 5408. The x-ray, radio and optical fluxes as well as the x-ray spectral shape are consistent with beamed relativistic jet emission from an accreting stellar black hole. If confirmed, this would suggest that the ultraluminous x-ray sources may be stellar-mass rather than intermediate mass black holes. However, interpretation of the source as a jet-producing intermediate-mass black hole cannot be ruled out at this time.

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arXiv2002

X-Ray Jet Emission from the Black Hole X-Ray Binary XTE J1550-564 with Chandra in 2000

We have discovered an X-ray jet due to material ejected from the black hole X-ray transient XTE J1550-564. The discovery was first reported by Corbel et al. (Science, 298, 196 and astro-ph/0210224), and here, we present an analysis of the three Chandra observations made between 2000 June and 2000 September. For these observations, a source is present that moves in an eastward direction away from the point source associated with the compact object. The separation between the new source and the compact object changes from 21.3 arcseconds in June to 23.4 arcseconds in September, implying a proper motion of 21.2 +/- 7.2 mas/day, a projected separation of 0.31-0.85 pc and an apparent jet velocity between 0.34 +/- 0.12 and 0.93 +/- 0.32 times the speed of light for a source distance range of d = 2.8-7.6 kpc. These observations represent the first time that an X-ray jet proper motion measurement has been obtained for any accretion powered Galactic or extra-galactic source. While this work deals with the jet to the east of the compact object, the western jet has also been detected in the X-ray and radio bands. The most likely scenario is that the eastern jet is the approaching jet and that the jet material was ejected from the black hole in 1998. Along with a 1998 VLBI proper motion measurement, the Chandra proper motion indicates that the eastern jet decelerated between 1998 and 2000. We present results on the morphology and energy spectrum of the jet. We cannot definitively determine the X-ray emission mechanism, but a synchrotron origin is viable and may provide the simplest explanation for the observations.

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arXiv2001

X-Ray Observations of XTE J1550-564 During the Decay of the 2000 Outburst - I. Chandra and RXTE Energy Spectra

We report on the evolution of the X-ray energy spectrum for the black hole candidate (BHC) X-ray transient XTE J1550-564 during the decay of the 2000 outburst. The Rossi X-ray Timing Explorer (RXTE) and Chandra observations span nearly five orders of magnitude in luminosity. The RXTE spectra are dominated by a power-law component and a comparatively weak soft component was also detected for the first two observations. The source made a transition to the canonical hard state near a luminosity of 9E36 erg/s over several observations as evidenced by a drop in the flux of the soft component in the RXTE energy band and a hardening of the power-law component to a photon index near 1.6. The power-law did not exhibit this behavior for the previous XTE J1550-564 outburst. For some observations, we detect a high energy cutoff and find that the cutoff is more significant and at lower energy during the transition than in the hard state. The cutoff in the hard state is at higher energy than has been seen for most previous accreting BHCs. The Chandra spectrum provides evidence for spectral evolution after the hard state transition. It is well, but not uniquely, described by a power-law with a photon index of 2.30^{+0.41}_{-0.48} (90% confidence) and interstellar absorption. Advection-dominated accretion flow models predict gradual spectral softening as the luminosity drops, but our observations do not allow us to determine if the spectral evolution is gradual or sudden. The lowest luminosity we measure for XTE J1550-564 with Chandra is 5E32 erg/s (0.5-7 keV, for a distance of 4 kpc). Although this is probably not the true quiescent luminosity, it represents a useful upper limit on this quantity.

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arXiv1999

Quenching of the radio jet during the X-ray high state of GX 339-4

We have observed the black hole candidate X-ray binary GX 339-4 at radio wavelengths before, during and after the 1998 high/soft X-ray state transition. We find that the radio emission from the system is strongly correlated with the hard X-ray emission and is reduced by a factor > 25 during the high/soft state compared to the more usual low/hard state. At the points of state transition we note brief periods of unusually optically-thin radio emission which may correspond to discrete ejection events. We propose that in the low/hard state black hole X-ray binaries produce a quasi-continuous outflow, in the high/soft state this outflow is suppressed, and that state transitions often result in one or more discrete ejection events. Future models for low/hard states, such as ADAF/ADIOS solutions, need to take into account strong outflow of relativistic electrons from the system. We propose that the inferred Comptonising corona and the base of the jet-like outflow are the same thing, based upon the strong correlation between radio and hard X-ray emission in GX 339-4 and other X-ray binaries, and the similarity in inferred location and composition of these two components.

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