The large-scale diffuse radio emission in A781

TL;DR

This study investigates diffuse radio emission in galaxy cluster A781, revealing a central radio halo and a peripheral relic with spectral steepening, indicating complex intra-cluster medium activity.

Contribution

First detailed analysis of diffuse radio emission in A781, identifying a radio halo and a relic with spectral properties, enhancing understanding of cluster radio phenomena.

Findings

Detected a central radio halo with typical properties.

Identified a peripheral relic with spectral steepening.

Linked the relic to a previously observed patch.

Abstract

A781 belongs to a complex system characterized by extended X-ray emissions that may form part of line of clusters of galaxies along a filament. The aim of this work is to investigate the possible presence of extended, diffuse synchrotron radio emission connected to the intra-cluster medium of A781. We studied the radio continuum emission and the spectral index properties in proximity of the A781 by analyzing archival Very Large Array observations at 1400 and 325 MHz. The main cluster of the system is permeated by diffuse low-surface brightness radio emission which is classified, being located close to the center, as a radio halo. The diffuse emission presents the typical extension and radio power of the other halos known in the literature. Interestingly, the radio halo appears to be linked to a peripheral patch previously found in the literature. The spectrum of this peripheral emission shows a radial steepening which may confirm that this source is indeed a cluster relic.