Nonthermal emission from the radio relic of the galaxy cluster A2256

TL;DR

This paper models non-thermal emissions from the radio relic in galaxy cluster A2256, estimating magnetic fields, cosmic ray densities, and predicting gamma-ray and radio fluxes based on shock-related relic formation.

Contribution

It provides a detailed analysis of the relic's non-thermal emissions, estimating magnetic field strength and cosmic ray densities, and predicts gamma-ray and radio fluxes for the first time.

Findings

Magnetic field strength in the relic is about 0.05 μG.

Electron density varies from 3 x 10^{-4} to 3 x 10^{-5} cm^{-3}.

Predicted radio fluxes are ~6 Jy at 60MHz and ~10 Jy at 30MHz.

Abstract

We aim to obtain a consistent description of non-thermal emissions from Abell 2256 and to give a prediction for a gamma-ray emission from this galaxy cluster. Assuming that a radio relic illuminates a localization of an ongoing merger, and that both radio and non-thermal part of hard X-ray emission are due to electron component of cosmic rays filling the relic, we derived from radio and hard X-ray properties of the relic in A2256 the magnetic field strength and number densities for relativistic electrons and protons. Due to the interpretation of the radio relic as a structure formed just where a shock front is, we discuss a gamma-ray emission at the cluster periphery. The estimated strength of the magnetic field in the relic is equal to 0.05 \muG, while the amplitude of the electron number density varies from 3 x 10^{-4} to 3 x 10^{-5} cm^{-3} (respectively for the relic thickness of 50 to 500 kpc). We got a substantial degree of non-equipartition between cosmic rays and magnetic field in the relic region, where the CR pressure is approaching that of thermal gas. Our prediction for LOFAR is a synchrotron flux from the relic region of the order of \sim 6 Jy at 60MHz and \sim 10 Jy at 30MHz. The lower limit of the gamma-ray flux from the relic region calculated for a hadronic channel is of the order of 10^{-12} erg cm^{-2}.