Formation of Relativistic Outflows in Shearing Black Hole Accretion Coronae

We examine the possibility that the relativistic jets observed in many activegalactic nuclei may be powered by the Fermi acceleration of protons in atenuous corona above a two-temperature accretion disk. In this picture theacceleration arises as a consequence of the shearing motion of the magneticfield in the corona, which is anchored in the underlying Keplerian disk. Theprotons in the corona have a power-law distribution because the density thereis too low for proton-proton collisions to thermalize the energy supplied viaFermi acceleration. The same shear acceleration mechanism also operates in thedisk itself, however, there the density is high enough for thermalization tooccur and consequently the disk protons have a Maxwellian distribution.Particle acceleration in the corona leads to the development of apressure-driven wind that passes through a critical point and subsequentlytransforms into a relativistic jet at large distances from the black hole. Wecombine the critical conditions for the wind with the structure equations forthe disk and the corona to obtain a coupled disk/corona/wind model. Using thecoupled model we compute the asymptotic Lorentz factor $\Gamma_\infty$ of thejet as a function of the cylindrical starting radius at the base of theoutflow, in the corona. Our results suggest that $\Gamma_\infty \lapprox 10$,which is consistent with observations of superluminal motion in blazars. Weshow that collisions between the jet and broad-line emission clouds can producehigh-energy radiation with a luminosity sufficient to power the $\gamma$-raysobserved from blazars. Subject headings: radiation mechanisms: non-thermal, accretion, accretiondisks, acceleration of particles, gamma rays: theoryComment: 50 pages, 13 figures, accepted by ApJ, 199