Correlated X-ray Spectral and Timing Behavior of the Black Hole Candidate XTE J1550-564

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  • 10 January 2000
Abstract
We present an analysis of data of the black hole X-ray transient XTE J1550-564, taken with RXTE between 1998 Nov 22 and 1999 May 20. The source went through several different states, which were divided into soft and hard states, based on the relative strength of the high energy power law tail. The states showed up as distinct branches in the color-color diagram, connecting to form a structure with a comb-like topology, the branch corresponding to the soft state forming the spine and the branches corresponding to the various hard states forming the teeth of the comb. The power spectral properties of each branch were correlated with their spectral properties. Three types of QPOs were found: 1-18 Hz and 100-285 Hz QPOs on the hard branches, and 15-18 Hz QPOs on and near the soft branch. The frequency of the high and low frequency QPOs on the hard branches were correlated with each other, and with spectral hardness. The behavior of the XTE J1550-564 strongly favors a two-dimensional description of black hole behavior, where the canonical soft high state is identified with regions near the spine of the comb in the color-color diagram and the canonical very high, intermediate, and low states with its teeth. The difference between the various hard states is associated with the flux of the blackbody component. The two parameters underlying this two-dimensional behavior, vary to a large extent independently, and could for example be the accretion rate through the disk and the size of the Comptonizing region causing the hard tail. We discuss how this picture could tie in with the canonical, one-dimensional behavior of black hole candidates that has usually been observed.

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