X-ray Spectral Variability of Black Hole Binaries

Abstract

Observations of black hole binaries in the X–ray/low γ–ray energy domain revealed complicated pattern of the spectral variability. The most prominent spectral changes are associated with well known and intensively studied transition between soft/hard spectral states (e.g. Tanaka, 1989, Grebenev et al., 1993, Sunyaev et al., 1993). This transitions manifest themselves as a dramatic redistribution of the emitted energy over wavelength (e.g. Fig.1). Along with these less evident “subtle” variations of the spectral properties are often observed (e.g. Fig.2). In many cases spectral changes are accompanied with changes in the short term aperiodic variability properties (e.g. Miyamoto et al., 1995, van der Klis, 1995, Belloni et al., 1996). The spectral and short term variability characteristics of the emission are directly measurable quantities, provided sufficient spectral and temporal resolution, sensitivity and energy coverage.