Shedding Light on the Spectral Variability of Black Hole Binaries Above 20 keV in the Hard State: Cygnus X-1

Details Shedding Light on the Spectral Variability of Black Hole Binaries Above 20 keV in the Hard State: Cygnus X-1 Shedding Light on the Spectral Variability of Black Hole Binaries Above 20 keV in the Hard State: Cygnus X-1

Jan 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21540402p&link_type=abstract

American Astronomical Society, AAS Meeting #215, #404.02; Bulletin of the American Astronomical Society, Vol. 42, p.225

Physics

Scientific paper

We present an analysis of extensive recent monitoring observations of the black hole X-ray binary Cygnus X-1 obtained as part of the Cygnus Region Key Program of the INTEGRAL mission. The observations span several two months long epochs between 2007 and 2009 spring. We concentrate on constraining the parameter range of the hard spectrum of black hole sources in the hard spectral state (see also contribution on GRS 1758-258 by A. Lohfink). 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.
Cygnus X-1 is one of only three persistent black hole binaries that spend most of their time in the hard spectral state. While its hard X-ray spectrum is one of the best studied examples for this source class and emission state, e.g., through our years long monitoring campaign with RXTE, the INTEGRAL monitoring allows us to study the spectral evolution over days and weeks which has only been sparsely sampled so far. We present long term lightcurves and an analysis of the evolution of the spectral parameters (empirical as well as based on thermal Comptonization) on timescales from about half an hour to three days. We search for the evidence of emission from non-thermal electrons, especially in spring 2009, when Cyg X-1 showed indications of softening and flaring, after spending 2.5 years in the hardest regime of its parameter space.

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