Cygnus X-1: shedding light on the spectral variability of black holes

Presentation duration: 15 minutes

Presenter: Victoria Grinberg

We present an analysis of extensive recent monitoring observations of the high mass black hole X-ray binary Cygnus X-1 obtained as part of the 2007 to 2011 Key Programme observations of the INTEGRAL mission. Cyg X-1 is one of only three persistent black hole binaries in our galaxy that spend most of their time in the hard spectral state. After spending ~3 years in the hardest regime of its parameter space, the source displayed a softening and flaring episode in mid 2009 and entered an on-going soft state in early 2010 June. 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. The parameter ranges for hard and soft state are constrained and discussed with a special focus on the comparison with previous observations of both Cyg X-1 itself and transient sources, where such measurements, which are important in order to understand the physics of the hot plasma of the jet base and/or the corona, are typically difficult to obtain with high accuracy. Furthermore we touch upon possible polarization measurements of Cyg X-1 with INTEGRAL/IBIS.