A time-dependent model for high energy emission of blazars

Abstract

We present a time-dependent model of the high energy emission of blazars based on a pair creation instability that can develop spontaneously in the two-flow model. In this scenario, a relativistic pair plasma is generated inside a mildly relativistic jet emitted by an accretion disk. Pairs cool by Synchrotron Self Compton (SSC) and External Compton (EC) process and produce gamma-rays that are self absorbed to produced new pairs. Thanks to continuous reacceleration by the MHD turbulence, a pair runaway instability can develop, which can saturate only through the damping of turbulence. We adopt a simple prescription to describe this effect. In some regime, a limiting cycle can develop, with oscillations of pair densities and turbulence level along the jet, producing flares in high energy emission and at other wavelengths. Although calculations have been carried out assuming a power law distribution of particles, it seems that a pile-up distribution could better account for TeV BL Lacs.