Modelling of blazar SEDs with the nonlinear SSC cooling process

TL;DR

This paper analytically models the nonlinear, time-dependent SSC cooling process in blazar jets, revealing new spectral features and the significant potential impact of SSC in FSRQs, challenging previous assumptions based on linear models.

Contribution

It provides the first analytical analysis of nonlinear, time-dependent SSC effects on blazar SEDs, including external Compton cooling in a unified framework.

Findings

Spectral features differ markedly from linear models.

SSC can significantly influence FSRQ emission.

External Compton flux depends strongly on parameters.

Abstract

Observations of blazar flaring states reveal remarkably different variability time scales. Especially rapid flares with flux doubling time scales of the order of minutes have been puzzling for quite some time. Many modeling attempts use the well known linear relations for the cooling and emission processes in the jet in a steady-state scenario, albeit the obvious strongly time-dependent nature of flares. Due to the feedback of self-produced radiation with additional scattering by relativistic electrons, the synchrotron-self Compton (SSC) effect is inherently time-dependent. Although this feedback is usually implemented in numerical treatments, only recently an analytical analysis of the effects of this nonlinear behaviour has been performed. Here, we report our results concerning the effect of the time-dependent SSC on the spectral energy distribution (SED) of blazars. We calculated analytically the synchrotron and the SSC component, giving remarkably different spectral features compared to the standard linear approach. Adding an external photon field to the original setting, we could implement quite easily the effect of an additional external Compton (EC) cooling, since such strong external photon fields are observed in flat spectrum radio quasars (FSRQ), a subclass of blazars. Calculating the resulting flux due to the EC cooling, we were able to show that the resulting inverse Compton component strongly depends on the free parameters, and that SSC could potentially have a strong effect in FSRQs, contrary to what is usually assumed.