Spectral index maps of radio halos and relics

Abstract

AbstractNew VLA observations at 90 cm are presented for the clusters of galaxies Abell 2219 and Abell 2744, which are characterized by the presence of a radio halo and relic. These sources are suggested to originate from particles reaccelerated in the cluster central regions, possibly by turbulence following major merger events. The study of the spectral properties of these sources is of great importance for the knowledge of the characteristics of relativistic particles and magnetic fields on large scales. Combining images at 90 and 20 cm, we obtained the spectral index distribution of the diffuse radio sources with a resolution of 1′.We produced radial brightness profiles at the two wavelengths, from which we calculated the radial spectral index trend. Our main result is that the spectral index shows a steepening with increasing distance from the cluster center to the edge. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)