Particle Acceleration in (by) Accretion Discs
  I present a model for acceleration of protons by the second-order Fermi process acting on randomly scrambled magnetic flux arches above an accretion disc. The accelerated protons collide with thermal protons in the disc, producing degraded energetic protons, charged and neutral pions, and neutrons. The pions produce gamma-rays by spontaneous decay of $\pi^0$ and by bremsstrahlung and Compton processes following the decay of $\pi^\pm$ to $e^\pm$. 
J. I. Katz