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 the former has been explored extensively, the latter is in its infancy. In this 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 shock/dissipation lifetime, electron-injection time profile, adiabaticity, and half-opening angle of the jet. In particular, we demonstrate the large difference between flare profiles produced in the radiative and adiabatic regimes. We apply our model to the ~1 day timescale flares observed in optically violently variable quasars, checking whether the external radiation Compton (ERC) model for γ-ray flares at energies greater than 30 MeV (EGRET range) can be reconciled with the flares observed at lower energies. Specifically, we show that the strict correlation between X-ray and γ-ray flares strongly supports the dominance of the synchrotron self-Compton mechanism in the X-ray band. We also derive conditions that must be satisfied by the ERC model in order to explain a lag of the γ-ray peak behind 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 certain energy, the flares should decay significantly more slowly in the soft γ-ray band than at energies greater than 30 MeV.