Correlation Between BATSE Hard X-ray Spectral and Timing Properties of   Cygnus X-1
  We have analyzed approximately 1100 days of Cygnus X-1 hard X-ray data obtained with BATSE to study its rapid variability. We find for the first time correlations between the slope of the spectrum and the hard X-ray intensity, and between the spectral slope and the amplitude of the rapid variations of the hard X-ray flux. We compare our results with expectations from current theories of accretion onto black holes. 
D.J. Crary, C. Kouveliotou, J. van Paradijs, F. van der Hooft, D.M.   Scott, W.S. Paciesas, M. van der Klis, M.H. Finger, B....