Hard X-ray and radio observations of Abell 754

¹ Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF), CNR, via del Fosso del Cavaliere 100, 00133 Roma, Italy e-mail: dario@rm.iasf.cnr.it
² IASF, CNR, Bologna, Italy
³ Osservatorio Astronomico di Brera, Merate, Italy
⁴ IASF, CNR, Milano, Italy
⁵ Istituto di Radioastronomia, CNR, Bologna, Italy
⁶ Dip. di Astronomia, Univ. di Bologna, Bologna, Italy

Corresponding author: R. Fusco-Femiano, dario@rm.iasf.cnr.it

Received: 2 July 2002
Accepted: 3 November 2002

Abstract

We present a long BeppoSAX observation of Abell 754 that reports a nonthermal excess with respect to the thermal emission at energies greater than ~45 keV. A VLA radio observation at 1.4 GHz definitely confirms the existence of diffuse radio emission in the central region of the cluster, previously suggested by images at 74 and 330 MHz (Kassim et al. 2001), and reports additional features. Besides, our observation determines a steeper radio halo spectrum in the 330-1400 MHz frequency range with respect to the spectrum detected at lower frequencies, indicating the presence of a spectral cutoff. The presence of a radio halo in A754, considered the prototype of a merging cluster, reinforces the link between formation of Mpc-scale radio regions and very recent or current merger processes. The radio results combined with the hard X-ray excess detected by BeppoSAX give information on the origin of the electron population responsible for nonthermal phenomena in galaxy clusters. We discuss also the possibility that 26W20, a tailed radio galaxy with BL Lac characteristics located in the field of view of the PDS, could be responsible for the observed nonthermal hard X-ray emission.