External Compton emission in blazars of non-linear SSC cooled electrons

TL;DR

This paper compares the external Compton and non-linear SSC models for blazar high-energy emissions, showing that electron cooling processes significantly influence the dominance of SSC or EC components in their spectral energy distributions.

Contribution

It provides an analytical comparison of external Compton and non-linear SSC models, highlighting the impact of electron cooling mechanisms on blazar emission components.

Findings

Non-linear SSC cooling can produce powerful inverse Compton components.

Electron cooling type influences whether SSC or EC dominates the SED.

Time-dependent treatment is crucial for accurate blazar flare modeling.

Abstract

The origin of the high-energy component in spectral energy distributions (SED) of blazars is still a bit of a mystery. While BL Lac objects can be rather successfully modelled within the one-zone synchrotron self-Compton (SSC) scenario, the SED of low peaked Flat Spectrum Radio Quasars (FSRQ) is more difficult to reproduce. Their high-energy component needs the abundance of strong external photon sources, giving rise to stronger cooling via the inverse Compton channel, and thusly to a powerful component in the SED. Recently, we were able to show that such a powerful inverse Compton component can also be achieved within the SSC framework. This, however, is only possible if the electrons cool by SSC, which results in a non-linear process, since the cooling depends on an energy integral over the electrons. In this paper we aim to compare the non-linear SSC framework with the external Compton (EC) output by calculating analytically the external Compton component with the underlying electron distribution being either linearly or non-linearly cooled. Due to the additional linear cooling of the electrons with the external photons, higher number densities of electrons are required to achieve non-linear cooling, resulting in more powerful inverse Compton components. If the electrons initially cool non-linearly, the resulting SED can exhibit a dominating SSC over the EC component. However, this dominance depends strongly on the input parameters. We conclude that with the correct time-dependent treatment the SSC component should be taken into account to model blazar flares.