A Combined Model for the X-Ray to Gamma-Ray Emission of Cygnus X-1

We use recent data obtained by three (OSSE, BATSE, and COMPTEL) of four instruments on board the Compton Gamma Ray Observatory (CGRO) to construct a model of Cyg X-1 that describes its emission in a broad energy range, from soft X-rays to MeV γ-rays, self-consistently. The γ-ray emission is interpreted to be the result of Comptonization, bremsstrahlung, and positron annihilation in a hot, optically thin, and spatially extended region surrounding the whole accretion disk. For the X-ray emission, a standard corona-disk model is applied. We show that the Cyg X-1 spectrum accumulated by the CGRO instruments during a ~4 year time period between 1991 and 1995, as well as the HEAO 3 γ1 and γ2 spectra, can be well represented by our model. The derived parameters match the observational results obtained from X-ray measurements.