Synchrotron Self‐Comptonization in a Relativistic Collision Front Model

Abstract

We study the radiation yield of the synchrotron self-Compton (SSC) process in the framework of the relativistic collision front model proposed by Pohl & Schlickeiser. In that model, the decay of neutral pions is a prominent process, in particular concerning the TeV-scale γ-ray emission. The SSC process must occur at some level in all blazars, however, on account of the strong radiation field in the jet provided by the synchrotron cooling of the simultaneously produced secondary electrons and positrons from charged pion decay. We investigate the influence of the parameters of the relativistic collision front and the ambient matter on the spectral evolution of the blazar emission, and we present multiwavelength spectra, light curves, and flux ratios for a few characteristic situations. We also consider the effects on the temporal evolution of the multiband spectra of AGNs caused by the additional cooling high-energy electrons due to the SSC emission. Our results indicate that the SSC radiation provides the decisive contribution to the GeV range of AGN emission spectra, whereas the π⁰ decay provides γ-rays at the highest energies in the TeV band. The synchrotron radiation at keV energies, the SSC emission in the GeV range, and the π⁰ decay component in the TeV band can vary on the same short timescales on account of small-scale structure in the interstellar medium of the AGN host galaxies and hence rapid fluctuations in the injection rate of relativistic protons. This behavior would be very difficult to explain in a purely leptonic SSC model. When the light curves are smoothed over small to medium timescales, the GeV-to-keV and the TeV-to-keV flux ratios show a characteristic long-term evolution that depends on the jet aspect angle and the initial jet Lorentz factor. Our results emphasize the need for AGN observations at GeV energies, e.g., by the upcoming GLAST mission, to complement the ongoing blazar monitoring by satellite X-ray detectors and ground-based Cerenkov telescopes that cover the TeV band.