A model for the high-energy emission of Cyg X-1

We construct a model of Cyg X-1 which describes self-consistently its emission from soft X-rays to MeV γ-rays. Instead of a compact pair-dominated γ-ray emitting region, we consider a hot optically thin and spatially extended proton-dominated cloud surrounding the whole accretion disc. The γ-ray emission is due to bremsstrahlung, Comptonization, and positron annihilation, while the corona-disc model is retained for the X-ray emission. We show that the Cyg X-1 spectrum accumulated by OSSE, BATSE, and COMPTEL in 1991-95, as well as the HEAO-3 γ₁ and γ₂ spectra can be well fitted by our model (see [1] for details). The derived parameters are in qualitative agreement with the picture in which the spectral changes are governed by the mass flow rate in the accretion disc. In this context, the hot outer corona could be treated as the advection-dominated flow co-existing with a standard thin accretion disc.