215th AAS Meeting

Washington, DC, USA
2010 January 3–7

Shedding light on the spectral variability of black hole binaries above 20 keV in the hard state: Cygnus X-1

Katja Pottschmidt, D.M. Marcu, V. Grinberg, J. Wilms, M. Cadolle-Bel, F. Fürst, M. Hanke, M.A. Nowak, S. Markoff, J.A. Tomsick, J. Rodriguez, G.G. Pooley

We present an analysis of extensive recent monitoring observations of the black hole X-ray binary Cyg X-1 obtained as part of INTEGRAL's Cygnus Region Key Programme. The observations span several two-month long epochs between 2007 and 2009. We focus on constraining the parameter range of the hard spectrum of black hole sources in the hard spectral state (see also poster on GRS 1758-258 by A. Lohfink et al.). This range is not yet well known, as it is difficult to measure to high accuracy for transient sources, but it is important to know in order to understand the physics of the hot plasma of the jet and/or corona. Cyg X-1 is one of three persistent black hole binaries that spend most of their time in the hard spectral state.