Gamma rays from galactic black hole candidates with stochastic particle acceleration

We consider stochastic particle acceleration in plasmas around stellar mass black holes to explain the emissions above 1 MeV from Galactic black hole candidates. We show that for certain parameter regimes, electrons can overcome Coulomb losses and be accelerated beyond the thermal distribution to form a new population, the distribution of which is broad and is usually not a power law; the peak energy of the distribution is determined by the balance between acceleration and cooling, with particles piling up around it. Radiation by inverse-Compton scattering off the thermal (from background) and nonthermal (produced by acceleration) particles can in principle explain the hard X-ray to gamma-ray emissions from black hole candidates. We present model fits of Cyg X-1 and GRO J0422 in the 50 keV-5 MeV region observed with OSSE and COMPTEL.