The Curious Case of Abell 2256

TL;DR

This study combines radio and X-ray observations to analyze the complex merger activity and intracluster medium structures of galaxy cluster Abell 2256, revealing insights into shock origins and cold front dynamics.

Contribution

It provides new multi-wavelength data and analysis of Abell 2256's merger-related features, including spectral index gradients and intracluster medium structures.

Findings

Spectral index steepens across relics, indicating shock acceleration.

X-ray maps show low-pressure core and multiple cool regions.

Cold fronts exhibit similar motion directions.

Abstract

Abell 2256 is a rich, nearby (z=0.0594) galaxy cluster that has significant evidence of merger activity. We present new radio and X-ray observations of this system. The low-frequency radio images trace the diffuse synchrotron emission of the Mpc-scale radio halo and relics as well as a number of recently discovered, more compact, steep spectrum sources. The spectral index across the relics steepens from the north-west toward the south-east. Analysis of the spectral index gradients between low and and high-frequencies shows spectral differences away from the north-west relic edge such that the low-frequency index is significantly flatter than the high frequency spectral index near the cluster core. This trend would be consistent with an outgoing merger shock as the origin of the relic emission. New X-ray data from XMM-Newton reveal interesting structures in the intracluster medium pressure, entropy and temperature maps. The pressure maps show an overall low pressure core co-incident with the radio halo emission, while the temperature maps reveal multiple regions of cool emission within the central regions of Abell 2256. The two cold fronts in Abell 2256 both appear to have motion in similar directions.