The large-scale diffuse radio emission in A781

Context. 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. Aims. 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. Methods. We studied the radio continuum emission and the spectral index properties in the proximity of A781 by analyzing archival Very Large Array observations at 1400 and 325 MHz. Results. The main cluster of the system is permeated by diffuse low-surface brightness radio emission which is classified as a radio halo because it is located close to the center. 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 that was 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.