RELATIVISTIC ELECTRON-POSITRON BEAM FORMATION IN THE FRAMEWORK OF THE 2-FLOW MODEL FOR ACTIVE GALACTIC NUCLEI

We propose a model for relativistic beam formation in active galactic nuclei, in which electrons and positrons are generated by pair cascade on the UV photons of the accretion disk. In situ turbulent acceleration by Alfven waves in a pair plasma balances the Compton losses and prevents annihilation. The origin of the turbulence is in the subrelativistic magnetohydrodynamic accretion ejection flow, which guarantees an extended energy reservoir up to distances where the Compton drag becomes inefficient. We show that, above some threshold of the turbulence level, easily achieved, the pair creation becomes catastrophic, and so the dramatic increase of the relativistic pressure expels the pair plasma along the widening flux tubes. Bulk Lorentz factors between 3 and 20 are obtained, in good agreement with observations. Moreover, the model provides a natural explanation of the decentered location of the hard X-ray sources suggested by the strong iron line and the reflected component of this spectra. Most of the turbulence energy is transferred to the X-rays, and a much smaller fraction is converted into beam kinetic energy, which is enough to account for the power involved in VLBI knots.