Deciphering the spectral properties of the atypical radio relic in A115 using uGMRT, VLA, and LOFAR

TL;DR

This study investigates the complex spectral properties of an atypical radio relic in galaxy cluster A115 using multi-frequency radio observations, supporting the shock front origin hypothesis from an off-axis merger.

Contribution

It provides a detailed multi-frequency analysis of the A115 relic, offering new insights into its formation mechanism and spectral characteristics.

Findings

Supports shock front origin from off-axis merger

Re-energization of old particle populations observed

Complex spectral properties analyzed

Abstract

The mega-parsec scale radio relics at the galaxy cluster periphery are intriguing structures. While textbook examples of relics posit arc-like elongated structures at the clusters' peripheries, several relics display more complex structures deviating from the conventional type. Abell 115 is a galaxy cluster, hosting an atypical radio relic at its northern periphery. Despite the multi-wavelength study of the cluster over the last decades, the origin of the radio relic is still unclear. In this paper, we present a multi-frequency radio study of the cluster to infer the possible mechanism behind the formation of the radio relic. We used new 400 MHz observations with the uGMRT, along with archival VLA 1.5 GHz observations and archival LOFAR 144 MHz observations. Our analysis supports the previous theory on the relic's origin from the passage of a shock front due to an off-axis merger, where the old population of particles from the radio galaxies at the relic location has been re-energised to illuminate the 2 Mpc radio relic.