Radio relics radio emission from multi-shock scenario

TL;DR

This study explores how multiple shock acceleration in galaxy cluster outskirts can produce radio relics with distinct spectra and higher emission, aligning with observations and detectable by current radio telescopes.

Contribution

It introduces a multi-shock acceleration scenario that explains the spectral shape and enhanced radio emission of relics, differing from single-shock models.

Findings

Electrons shocked multiple times develop a unique energy spectrum.

Radio emission in the multi-shock scenario is an order of magnitude higher.

Simulated relics follow a KGJP spectral shape consistent with observations.

Abstract

Radio relics are giant ($\sim$Mpc) synchrotron sources that are believed to be produced by the (re)acceleration of cosmic-ray electrons (CRe) by shocks in the intracluster medium. In this numerical study, we focus on the possibility that some radio relics may arise when electrons undergo diffusive shock acceleration at multiple shocks in the outskirts of merging galaxy clusters. This multi-shock (MS) scenario appears viable to produce CRe that emit visible synchrotron emission. We show that electrons that have been shocked multiple times develop an energy spectrum that significantly differs from the power-law spectrum expected in the case of a single shock scenario. As a consequence, the radio emission generated by CRe that shocked multiple times is higher than the emission produced by CRe that are shocked only once. In the case explored in this paper, the radio emission produced in the two scenarios differ by one order of magnitude. In particular in the MS scenario, the simulated relic follows a KGJP spectral shape, consistent with observation. Furthermore, the produced radio emission is large enough to be detectable with current radio telescopes (e.g. LOFAR, JVLA).