The discovery of diffuse steep spectrum sources in Abell 2256

Abstract

Context: Hierarchical galaxy formation models indicate that during their lifetime galaxy clusters undergo several mergers. Here we report on the discovery of three diffuse radio sources in the periphery of Abell 2256, using the GMRT. Aims: The aim of the observations was to search for diffuse ultra-steep spectrum radio sources within the galaxy cluster Abell 2256. Methods: We have carried out GMRT 325 MHz radio continuum observations of Abell 2256. V, R and I band images of the cluster were taken with the 4.2m WHT. Results: We have discovered three diffuse elongated radio sources located about 1 Mpc from the cluster center. Two are located to the west of the cluster center, and one to the southeast. The sources have a measured physical extent of 170, 140 and 240 kpc, respectively. The two western sources are also visible in deep low-resolution 115-165 MHz WSRT images, although they are blended into a single source. For the combined emission of the blended source we find an extreme spectral index of -2.05\pm 0.14 between 140 and 351 MHz. The extremely steep spectral index suggests these two sources are most likely the result of adiabatic compression of fossil radio plasma due to merger shocks. Conclusions: The discovery of the steep spectrum sources implies the existence of a population of faint diffuse radio sources in (merging) clusters with such steep spectra that they have gone unnoticed in higher frequency (\gtrsim 1 GHz) observations. An exciting possibility therefore is that such sources will determine the general appearance of clusters in low-frequency high resolution radio maps as will be produced by for example LOFAR or LWA.

5 pages, 2 figures, accepted for publication in A&A on October 16, 2009

References in corpus (5)

• Observations of extended radio emission in clusters
• Deep 1.4 GHz VLA Observations of the Radio Halo and Relic in Abell 2256
• The duty cycle of local radio galaxies
• Deep Westerbork observations of Abell 2256 at 350 MHz
• Relics of Double Radio Sources

Cited by in corpus (19)

• Diffuse Radio Emission from Galaxy Clusters
• The duty cycle of radio-mode feedback in complete samples of clusters
• First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256
• Wideband VLA Observations of Abell 2256 I: Continuum, Rotation Measure and Spectral Imaging
• Chandra and JVLA observations of HST Frontier Fields cluster MACS J0717.5+3745
• LOFAR and APERTIF surveys of the radio sky: probing shocks and magnetic fields in galaxy clusters
• The diffuse radio filament in the merging system ZwCl 2341.1+0000
• Deep low-frequency radio observations of Abell 2256 I: The filamentary radio relic
• A multiwavelength view of the galaxy cluster Abell 523 and its peculiar diffuse radio source
• The spectral index image of the radio halo in the cluster Abell 520 hosting a famous bow shock
• Spectral Index Studies of the Diffuse Radio Emission in Abell 2256: Implications to Merger Activity
• Deep low-frequency radio observations of Abell 2256 II: The ultra-steep spectrum radio halo
• Chandra View of the Ultra-Steep Spectrum Radio Source in Abell 2443: Merger Shock-Induced Compression of Fossil Radio Plasma?
• The dynamical status of ZwCl 2341.1+0000: a very elongated galaxy structure with a complex radio emission
• Ultra-Steep Spectrum Radio `Jellyfish' Uncovered in Abell 2877
• JVLA S and X-band Polarimetry of the Merging Cluster Abell 2256
• Particle re-acceleration and diffuse radio sources in the galaxy cluster Abell 1550
• The Double Galaxy Cluster Abell 2465 I. Basic Properties: Optical Imaging and Spectroscopy
• Probing particle acceleration in Abell 2256: from to 16 MHz to gamma rays