X-ray Astronomy 2009

Bologna, Italy
2009 September 7–11

Properties of a fast state transition in Cygnus X-1

Moritz Böck, Jörn Wilms, Victoria Grinberg, Katja Pottschmidt, Manfred Hanke, Sera Markoff, Michael A. Nowak, Stefan Pirner, Refiz Duro, Guy Pooley

In 2005 February we observed the microquasar Cygnus X-1 for a total of 10 days quasi-continuously with the Rossi X-ray Timing Explorer and the Ryle telescope. During that period of time Cyg X-1 was very variable and covered a large fraction of its total variability found during our years long monitoring. A full transition from the hard to the soft state occured within less than 2.5 hours. We present results of the spectral and timing analy- sis, compare them with the long-term behavior and discuss the discovered energy dependence of the power spectra.