Hintze Centre for Astrophysical Surveys

Abstract:

We present preliminary results on a global study of X-ray binaries using 14 Ms of data from the Rossi X-ray Timing Explorer RXTE satellite. Our initial study on GX 339-4 is recapped as an introduction to the methods used. We use a consistent analysis scheme for all objects, with three different spectral models to fit the powerlaw and disc components. We also take into account the possibility of a line being present in the data. The resulting almost 4000 observations allow the tracking of the spectral properties of the binaries as they evolve through an outburst. Our investigations concentrate on the disc and line properties of the binaries when in outburst. We also show the Disc-Fraction Luminosity diagram for the population of X-ray binaries studied which will enable us to further links with AGN. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

Abstract:

We report the discovery of a faint (Lx ∼ 4 ± 1.5 × 1037 ergs s-1, 0.5-2 keV), outflowing gaseous hot interstellar medium (ISM) in NGC 3379. This represents the lowest X-ray luminosity ever measured from a hot phase of the ISM in a nearby early-type galaxy. The discovery of the hot ISM in a very deep Chandra observation was possible thanks to its unique spectral and spatial signatures, which distinguish it from the integrated stellar X-ray emission, responsible for most of the unresolved emission in the Chandra data. This hot component is found in a region of ∼800 pc in radius at the center of the galaxy and has a total mass M ∼ 3 ± 1 × 105 M⊙. Independent theoretical prediction of the characteristics of an ISM in this galaxy, based on the intrinsic properties of NGC 3379, reproduce well the observed luminosity, temperature, and radial distribution and mass of the hot gas, and indicate that the gas is in an outflowing phase, predicted by models but not observed in any system so far.

Abstract:

Compact object displays drastic spectral and timing changing from the beginning to the end of an outburst, showing the different efficiencies of accretion processes. Black hole binaries hence exhibit schematically two different states in X-ray spectra: The first dominated by a thermal component and the second by a hard powerlaw shape like. Whereas the hard component is often attributed to the emission of a radiatively inefficient corona, the thermal component is interpreted as the emission of the optically thick accretion disc. The commonly accepted picture suggests that the observed transition between hard and soft states is associated by a drop in the accretion efficiency of the thermal component by a recession of the internal disc radius in hard states. However, recent studies based on relativistically broadened iron line and the thermal component strength analysis would tend to show the presence of the disc in the vicinity of the horizon. By a reanalysis of archive spectra where thermal emission is present, we tracked the values of the disc radii during outbursts among several sources. Indeed, whereas a constant inner radius would imply that the disc luminosity should monotonically depends on the temperature, we show that this relationship seems to deviate at the lowest luminosities. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.