Time Dependent Leptonic Modeling of Fermi II Processes in the Jets of Flat Spectrum Radio Quasars

Abstract: In this paper, we discuss the light-curve features of various flaring scenarios in a time-dependent leptonic model for low-frequency-peaked blazars. The quasar 3C273 is used as an illustrative example. Our code takes into account Fermi-II acceleration and all relevant electron cooling terms, including the external radiation fields generally found to be important in the modeling of the SEDs of FSRQs, as well as synchrotron self absorption and gamma-gamma pair-production. General parameters are constrained through a fit to the average spectral energy distribution (SED) of the blazar by numerically solving the time-dependent Fokker-Planck equation for the electron evolution in a steady-state situation. We then apply perturbations to several input parameters (magnetic field, particle injection luminosity, acceleration time scale) to simulate flaring events and compute time-dependent SEDs and light curves in representative energy bands (radio, optical, X-rays, gamma-rays). Time lags between different bands are evaluated using a discrete cross correlation analysis. We find that Fermi-II acceleration has a significant effect on the distributions and that flaring events caused by increased acceleration efficiency of the Fermi II process will produce a correlation between the radio, optical and gamma-ray bandpasses, but an anti-correlation between these three bandpasses and the X-ray band, with the X-rays lagging behind the variations in other bands by up to several hours.