Cygnus X-1: Shedding Light On The Spectral Variability Of The Hard State Of Black Holes
Abstract
We present an analysis of extensive recent monitoring observations of the black hole X-ray binary Cygnus X-1 obtained as part of the 2007 to 2009 Cygnus Region Key Program observations of the INTEGRAL mission. Cygnus X-1 is one of only three persistent black hole binaries that spend most of their time in the hard spectral state (see also contribution by A.M. Lohfink on INTEGRAL monitoring of GRS 1758-258). We concentrate on constraining the parameter range of the hard spectrum, a measurement that is typically difficult to obtain with high accuracy for transient sources, but which is important to know in order to understand the physics of the hot plasma of the jet base and/or the corona. While the hard X-ray spectrum of Cyg X-1 is one of the best studied examples of its kind, e.g., through our years long monitoring campaign with RXTE, the INTEGRAL monitoring allows us to study the spectral evolution from about half an hour over a few days to a few weeks, timescales that have been only sparsely sampled so far. After spending 3 years in the hardest regime of its parameter space (see also contribution by M.A. Nowak on multi-satellite hard state observations of Cyg X-1), the source displayed a softening and flaring episode in-mid 2009. We compare radio to X-ray broad band spectra (AMI, RXTE, INTEGRAL) of these two emission states.
- Publication:
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AAS/High Energy Astrophysics Division #11
- Pub Date:
- March 2010
- Bibcode:
- 2010HEAD...11.1102P