Spectral properties and origin of the radio halo in A3562

¹ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: tventuri@ira.cnr.it
² Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy
³ INAF - Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁴ Max-Planck-Institut für extraterrestrische Physik, 85740 Garching, Germany
⁵ National Centre for Radio Astrophysics (TIFR), Pune University Campus, Post Bag No. 3, Ganeshkhind, Pune 411 007, India

Received: 8 March 2005
Accepted: 20 May 2005

Abstract

We present a new detailed multiband study of the merging cluster A3562, in the core of the Shapley Concentration Supercluster. We analyzed new, low frequency radio data performed at 240 MHz, 332 MHz and 610 MHz with the Giant Metrewave Radio Telescope (GMRT). The new GMRT data allowed us to carry out a detailed study of the radio halo at the centre of A3562, as well as of the head–tail radio galaxy J1333–3141 embedded in it, and of the extended emission around the peripheral cluster galaxy J1332–3146a. Thanks to the present observations we could derive the integrated spectrum of the radio halo with five data points in the frequency range 240 MHz–1.4 GHz. Our data show a clear steepening of the total spectrum in this frequency range. Furthermore, by comparing the GMRT 332 MHz image with a previously published VLA 1.4 GHz image, we produced an image of the halo spectral index distribution. The image shows a very complex structure, with an average value of and a number of knots steepening up to ~2. We performed a combined morphological and statistical analysis using the radio images and the quantities derived from XMM-Newton and Chandra observations. We discuss our results in the light of particle re-acceleration processes in galaxy clusters. In particular, we outline an overall picture, consistent with the available radio and X-ray data, in which the cluster merger kinematics, the injection of turbulence and B–amplification induced by the merger between A 3562 and SC 1329–313 are jointly taken into account.