  We consider electron acceleration by obliquely propagating fast mode waves in
magnetically dominated accretion disk coronae. For low coronal plasma
densities, acceleration can exceed Coulomb drag at lower energies and energize
electrons out of the thermal background, resulting in a nonthermal tail. The
extent of this tail is determined by the balance between acceleration and
radiative cooling via inverse Compton scattering and synchrotron emission, and
usually goes out to tens of MeV. This will have direct applications for
explaining the gamma-rays from several galactic black hole candidates, such as
Cyg X-1 and GRO J0422, which show 0.5--5 MeV emissions in excess over what most
thermal models predict. Detailed time evolutions of the particle distributions
and wave spectra are also presented.
