Formation of Relativistic Outflows in Shearing Black Hole Accretion Coronae

Abstract

We examine the possibility that the relativistic jets observed in many active galactic nuclei may be powered by the Fermi acceleration of protons in a tenuous corona above a two-temperature accretion disk. In this picture the acceleration arises as a consequence of the shearing motion of the magnetic —eld in the corona, which is anchored in the underlying Keplerian disk. The protons in the corona have a power-law distribution because the density there is too low for proton-proton collisions to thermalize the energy supplied via Fermi acceleration. The same shear acceleration mechanism also operates in the disk itself; however, there the density is high enough for thermalization to occur and consequently the disk protons have a Maxwellian distribution. Particle acceleration in the corona leads to the development of a pressure-driven wind that passes through a critical point and subsequently transforms into a relativistic jet at large distances from the black hole. We combine the critical conditions for the wind with the structure equations for the disk and the corona to obtain a coupled disk-corona-wind model. Using the coupled model, we compute the asymptotic Lorentz factor of the jet as a function of the cylindrical starting radius at the base of the ! = out—ow, in the corona. Our results suggest that which is consistent with observations of super- ! = ( 10, luminal motion in blazars. We show that collisions between the jet and broad-line emission clouds can produce high-energy radiation with a luminosity sufficient to power the c-rays observed from blazars. Subject headings: acceleration of particlesaccretion, accretion disksgamma rays: theory ¨ radiation mechanisms: nonthermal