Abstract Details

Name: Rupal Basak
Affiliation: Nicolaus Copernicus Astronomical Center, Warsaw
Conference ID: ASI2017_545
Title : Spectral study of the hard state of GX 339-4 and Cygnus X-1
Authors and Co-Authors : Andrzej A. Zdziarski (Nicolaus Copernicus Astronomical Center, Warsaw)
Abstract Type : Oral
Abstract Category : Stars,ISM and the Galaxy
Abstract : The accretion disc geometry in the hard state of X-ray binaries (XRB) is a hotly debated topic with the main focus on whether the disc is truncated or not. We present a detailed analysis of all the spectral data of the black hole XRB source GX 339-4 in the hard state obtained by the XMM-Newton through 2004--2013. We model the spectrum with a thermal emission from the disc along with a Comptonization and the currently best reflection code, relxill. We modify the disc blackbody function in order to set the radius of the inner disc to that of the reflector. However, we find an unphysical behaviour of the truncation radius with the spectral hardness implying that the soft X-ray component is not simply a disc blackbody. Hence, we use this as a phenomenological model and fit the data in both full and reduced (higher energy) band. We test a large number of models e.g., that with a radial irradiation profile, adding unblurred reflection and assuming a lamppost geometry. In the coronal models, we find that the disc is highly truncated and the inner radius correlates with the spectral hardness which is fully consistent with the hard to soft transition of the truncated disc model. For the lamppost geometry as the radius could not be constrained, we fix it to the innermost stable orbit but then obtain large values of the source height. Hence, in all cases the relativistic effect is moderate. Finally, we find that in the softer states the degree of ionization is high which leads to strong spectral broadening and a broad iron line even though the relativistic effect is only moderate. Hence, the degree of ionization is a crucial parameter responsible for the broad line. A similar study is also presented for the high mass XRB source Cygnus X-1.