Electron Acceleration and the Production of Nonthermal Electron Distributions in Accretion Disk Coronae

Abstract

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.