Gamma-rays from synchrotron pair cascades in blazars?

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Abstract
The possibility of γ-ray production in blazars as a result of synchrotron e± pair cascade initiated by extremely high energy curvature photons in the disc/jet magnetic field is considered. It is assumed that the curvature radiation is produced by particles accelerated in the DC electric fields which are in turn induced during a reconnection process of the magnetic field in an accretion disc or a disc corona. if the reconnection region has a certain curvature, the acceleration of particles (electrons, protons) can be balanced by the particle energy losses on curvature radiation. As a result particles move through the reconnection region with an equilibrium Lorentz factor, and very efficiently transfer energy extracted from the electric field directly to extremely energetic curvature γ-rays. We concentrate on the case when the curvature photons are energetic enough so that they can develop synchrotron eγ pair cascades in the quantum domain in a perpendicular component of the magnetic field above the reconnection. We follow the development of such a cascade by using the Monte Carlo method. The γ-ray and e± spectra emerging from the cascade, and the γ-ray spectra from the complete cooling of secondary pairs in the local magnetic field are computed. Since the cascade saturates relatively close to the accretion disc we then consider the absorption of created γ-rays in the soft disc radiation. Depending on the disc radiation, which is determined by the black hole mass and the inner disc temperature, a part of the cascade γ-rays is absorbed creating the second generation of e± pairs. These pairs cool predominantly in the local magnetic field by the synchrotron process, emitting the second generation of γ-rays. Some of the most energetic second generation γ-rays can be further absorbed in the disc radiation producing tertiary e± pairs which cool by the synchrotron process as well. The optical depth for the tertiary photons produced in this last process is low so they can escape unabsorbed. We propose such a model as a possible explanation of huge, very short γ-ray outbursts observed from many blazars.

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