Long Term Variability of Cygnus X-1. IV. Spectral Evolution 1999-2004

J. Wilms, M. A. Nowak, K. Pottschmidt +2

(abbreviated abstract) We present the long term spectral evolution of the Galactic black hole candidate Cygnus X-1 in the X-rays and at 15GHz using ~200 pointed observations taken…