Spectral Transitions in Cygnus X-1 and Other Black Hole X-Ray Binaries

We show that the model proposed by Esin, McClintock, & Narayan for the low state, intermediate state, and high state of the black hole soft X-ray transient, Nova Muscae 1991, is consistent with the spectral evolution of the black hole X-ray binary, Cyg X-1, during the hard-to-soft state transition observed in 1996. We also apply the model to the outbursts of two other black hole X-ray transients, GRO J0422+32 and GRO J1719-24.