Comprehensive spectral analysis of Cyg X-1 using RXTE data

作     者：Rizwan Shahid Ranjeev Misra S.N.A.Jaaffrey 

作者机构：Department of PhysicsM.L.Sukhadia UniversityUdaipur-313001India Inter University Centre for Astronomy and AstrophysicsPune-411007India 

出 版 物：《Research in Astronomy and Astrophysics》 (天文和天体物理学研究（英文版）)

年 卷 期：2012年第12卷第10期

页      面：1427-1438页

核心收录：

学科分类：07[理学] 070401[理学-天体物理] 0704[理学-天文学] 

基　　金：funded by the ISRO-RESPOND program No:ISRO/RES/2/353/08-09 

主　　题：accretion accretion disks -- X-rays: binaries 

摘      要：We analyze a large number （〉 500） of pointed Rossi X-Ray Timing Explorer （RXTE） observations of Cyg X- 1 and model the spectrum of each one. A subset of the observations for which there is a simultaneous reliable measure of the hardness ratio by the All Sky Monitor shows that the sample covers nearly all the spectral shapes of Cyg X-1. Each observation is fitted with a generic empirical model consisting of a disk black body spectrum, a Comptonized component whose input photon shape is the same as the disk emission, a Gaussian to represent the iron line and a reflection feature. The relative strength, width of the iron line and the reflection parameter are in general correlated with the high energy photon spectral index F. This is broadly consistent with a geometry where for the hard state （low F ~ 1.7） there is a hot in- ner Comptonizing region surrounded by a truncated cold disk. The inner edge of the disk moves inwards as the source becomes softer till finally in the soft state （high F 〉 2.2） the disk fills the inner region and active regions above the disk produce the Comptonized component. However, the reflection parameter shows non-monotonic behavior near the transition region （F ~ 2）, which suggests a more complex geometry or physical state of the reflector. In addition, the inner disk temperature, during the hard state, is on average higher than in the soft one, albeit with large scatter. These inconsistencies could be due to limitations in the data and the empirical model used to fit them. The flux of each spectral component is well correlated with F, which shows that unlike some other black hole systems, Cyg X- 1 does not show any hysteresis be- havior. In the soft state, the flux of the Comptonized component is always similar to the disk one, which confirms that the ultra-soft state （seen in other brighter black hole systems） is not exhibited by Cyg X-1. The rapid variation of the Compton amplifica- tion factor with F naturally explains the absence of spec