Modeling the production of flares in gamma-ray quasars

Theories of high-energy radiation production in quasar jets can be verified by studies of both time-averaged spectra and variability patterns. While t he former has been explored extensively, the latter is in its infancy. In t his paper, we study the production of short-term flares in the shock-in-jet model. We examine how the flares' profiles depend on such parameters as sh ock/dissipation lifetime, electron-injection time profile, adiabaticity, an d half-opening angle of the jet. In particular, we demonstrate the large di fference between flare profiles produced in the radiative and adiabatic reg imes. We apply our model to the similar to1 day timescale flares observed i n optically violently variable quasars, checking whether the external radia tion Compton (ERC) model for gamma -ray flares at energies greater than 30 MeV (EGRET range) can be reconciled with the flares observed at lower energ ies. Specifically, we show that the strict correlation between X-ray and ga mma -ray flares strongly supports the dominance of the synchrotron self-Com pton mechanism in the X-ray band. We also derive conditions that must be sa tisfied by the ERC model in order to explain a lag of the gamma -ray peak b ehind the optical one, as claimed to be observed in PKS 1406-076. Finally, we predict that in ERC models where the MeV peak is related to the break in electron distribution owing to inefficient cooling of electrons below a ce rtain energy, the flares should decay significantly more slowly in the soft gamma -ray band than at energies greater than 30 MeV.