Short term X-ray rms variability of Cyg X-1
  A linear dependence of the amplitude of broadband noise variability on flux for GBHC and AGN has been recently shown by Uttley & McHardy (2001). We present the long term evolution of this rms-flux-relation for Cyg X-1 as monitored from 1998-2002 with RXTE. We confirm the linear relationship in the hard state and analyze the evolution of the correlation for the period of 1996-2002. In the intermediate and the soft state, we find considerable deviations from the otherwise linear relationship. A possible explanation for the rms-flux-relation is a superposition of local mass accretion rate variations. 
T. Gleissner (1), J. Wilms (1), K. Pottschmidt (2 and 3), P. Uttley   (4), M.A. Nowak (5), R. Staubert (1) ((1) IAA Tuebinge...