The very steep spectrum radio halo in Abell 697

Understand

In this paper we present a detailed study of the giant radio halo in the galaxy cluster Abell 697, with the aim to constrain its origin and connection with the cluster dynamics.

• We performed high sensitivity GMRT observations at 325 MHz, which showed that the radio halo is much brighter and larger at this frequency, compared to previous 610 MHz observations.
• In order to derive the integrated spectrum in the frequency range 325 MHz--1.4 GHz, we re--analysed archival VLA data at 1.4 GHz and made use of proprietary GMRT data at 610 MHz.
• {Our multifrequency analysis shows that the total radio spectrum of the giant radio halo in A\,697 is very steep, with $\alpha_{\rm~325 MHz}^{\rm~1.4 GHz} \approx 1.7-1.8$.