High energy emission from AGN cocoons in clusters of galaxies

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.

💡 Research Summary

The paper investigates high‑energy radiation that can be produced in the cocoons inflated by relativistic jets of young radio galaxies embedded in galaxy clusters. The authors adopt a simple but physically motivated model in which the kinetic power of the jet is continuously and adiabatically transferred into the cocoon as both internal energy and mass. By applying energy‑momentum conservation to the jet–cocoon system, they derive a direct relationship between the bulk Lorentz factor of the jet (Γ) and the thermal temperature of the cocoon electrons:

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