Some features of the direct and inverse double Compton effect as applied to astrophysics

TL;DR

This paper analyzes the inverse double Compton scattering process in astrophysics, deriving an analytical cross-section expression using QED, and highlights how the spectral characteristics of the photon source influence the process without infra-red divergences.

Contribution

It provides the first analytical expression for the inverse double Compton cross-section considering realistic photon source spectra and detailed balance, addressing infra-red divergence issues.

Findings

Inverse cross-section has no infra-red divergences at fixed photon energies.

The behavior of the inverse process depends on the spectral profile of the photon source.

The physical frequency profile is influenced by the intensity and line shape of incident radiation.

Abstract

In the present paper, we consider the process of inverse double Compton (IDC) scattering in the context of astrophysical applications. It is assumed that the two hard X-ray photons emitted from an astrophysical source are scattered on a free electron and converted into a single soft photon of optical range. Using QED S-matrix formalism for the derivation of a cross-section of direct double Compton (DDC) and assuming detailed balance conditions we give an analytical expression for the cross-section of the IDC process. It is shown that at fixed energies of incident photons the inverse cross-section has no infra-red divergences and its behavior is completely defined by the spectral characteristics of the photon source itself, in particular, by the finite interaction time of radiation with an electron. Thus, even for the direct process, the problem of resolving infrared divergence actually refers to a real physical source of radiation in which photons are never actually plane waves. As a result the physical frequency profile of the scattered radiation for direct as well as inverse double Compton processes is a function of both the intensity and line shape of the incident photon field.