High energy emission from AGN cocoons in clusters of galaxies

TL;DR

This paper predicts gamma-ray emissions from AGN cocoons in galaxy clusters, highlighting how jet dynamics influence thermal electron temperatures and resulting MeV-range Bremsstrahlung emissions.

Contribution

It introduces a model linking jet Lorentz factors to cocoon electron temperatures and predicts observable gamma-ray signatures from young radio galaxy cocoons.

Findings

Thermal electron temperature in cocoons is about MeV, determined by jet Lorentz factor.

Young cocoons can produce MeV-range thermal Bremsstrahlung emissions.

Hotter, GeV-range emissions are possible in younger sources.

Abstract

Gamma-ray emission from cocoons of young radio galaxies is predicted. Considering the process of adiabatic injection of the shock dissipation energy and mass of the relativistic jet into the cocoon, we find that the thermal electron temperature of the cocoon is typically predicted to be of the order of $\sim$ MeV, and is determined only by the bulk Lorentz factor of the jet. Together with the time-dependent dynamics of the cocoon expansion, we find that young cocoons can yield thermal Bremsstrahlung emissions at energies $\sim$MeV. Hotter cocoons (i.e., GeV) for younger sources are also discussed.