Seed photon fields of blazars in the internal shock scenario

Abstract

We extend our approach of modeling spectral energy distribution (SED) and light curves of blazars to include external Compton (EC) emission due to inverse Compton scattering of an external anisotropic target radiation field. We describe the time-dependent impact of such seed photon fields on the evolution of multifrequency emission and spectral variability of blazars using a multi-zone time-dependent leptonic jet model, with radiation feedback, in the internal shock model scenario. We calculate accurate EC-scattered high-energy (HE) spectra produced by relativistic electrons throughout the Thomson and Klein-Nishina regimes. We explore the effects of varying the contribution of (1) a thermal Shakura-Sunyaev accretion disk, (2) a spherically symmetric shell of broad-line clouds, the broad-line region (BLR), and (3) a hot infrared emitting dusty torus (DT), on the resultant seed photon fields. We let the system evolve to beyond the BLR and within the DT and study the manifestation of the varying target photon fields on the simulated SED and light curves of a typical blazar. The calculations of broadband spectra include effects of γ-γ absorption as γ-rays propagate through the photon pool present inside the jet due to synchrotron and inverse Compton processes, but neglect γ-γ absorption by the BLR and DT photon fields outside the jet. Thus, our account of γ-γ absorption is a lower limit to this effect. Here, we focus on studying the impact of parameters relevant for EC processes on HE emission of blazars