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Cluster Mergers and Diffuse Radio Emission in Abell 2256 and Abell 754

T. E. Clarke·T. A. Ensslin
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Abstract

We present deep VLA observations of the galaxy clusters Abell 2256 and Abell 754, both of which appear to be in the violent stage of major cluster merger events. The complex nature of Abell 2256 is revealed through radio images which, in addition to the head-tail galaxies, show two extended, irregular, and sharp-edged regions of diffuse radio emission at the cluster periphery (so called radio relics), and a large-scale diffuse radio halo located in the central regions of the cluster. Polarimetry of the A2256 cluster relics reveals large-scale ordered magnetic fields which appear to trace the bright filaments in the relics. The polarization fraction across the relics ranges from 20% - 40% with the majority of the relics polarized above the 30% level. At the sensitivity of our current observations we place an upper limit of 20% on the polarization of the radio halo. Low frequency VLA observations of Abell 754 reveal extended, diffuse radio (halo) emission in the cluster core region as well as steep spectrum emission in the cluster periphery. The location, morphology, and spectral index of the peripheral emission are consistent with the properties of radio relics. The X-ray evidence of the ongoing mergers in both clusters, together with the polarization properties of A2256's radio relics supports recent suggestions of a merger-induced origin of the relic emission. Deciphering the complex radio properties of these clusters may thus provide the key to understanding the dynamical history of the systems.

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T. E. Clarke, T. A. Ensslin. 2001-06-07. Cluster Mergers and Diffuse Radio Emission in Abell 2256 and Abell 754. https://arxiv.org/abs/astro-ph/0106137

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