Synchrotron Self‐Compton Model for Rapid Nonthermal Flares in Blazars with Frequency‐dependent Time Lags

We model rapid variability of multifrequency emission from blazars occurringacross the electromagnetic spectrum (from radio to gamma-rays). Lower energyemission is produced by the synchrotron mechanism, whereas higher energyemission is due to inverse Compton scattering of the synchrotron emission. Wetake into account energy stratification established by particle acceleration atshock fronts and energy losses due to synchrotron emission. We also considerthe effect of light travel delays for the synchrotron emission that suppliesthe seed photons for inverse Compton scattering. The production of a flare iscaused by the collision between a relativistic shock wave and a stationaryfeature in the jet (e.g., a Mach disk). The collision leads to the formation offorward and reverse shocks, which confine two contiguous emission regionsresulting in complex profiles of simulated flares. Simulations ofmultifrequency flares indicate that relative delays between the inverse Comptonflares and their synchrotron counterparts are dominated by energystratification and geometry of the emitting regions, resulting in both negativeand positive time delays depending on the frequency of observation. Lighttravel effects of the seed photons may lead to a noticeable delay of theinverse Compton emission with respect to synchrotron variability if the line ofsight is almost perfectly aligned with the jet. We apply the model to a flarein 3C 273 and derive the properties of shocked plasma responsible for theflare. We show that the pronounced negative time delay between the X-ray and IRlight curves (X-rays peak after the maximum in the synchrotron emission) can beaccounted for if both forward and reverse shocks are considered.Comment: 48 pages, 18 figures, accepted for publication in The Astrophysical Journa