Wideband VLA Observations of Abell 2256 I: Continuum, Rotation Measure and Spectral Imaging

TL;DR

This study uses wideband VLA observations to analyze the complex radio structures, spectral properties, and magnetic field variations in galaxy cluster Abell 2256, revealing filamentary features and potential magnetic reconnection processes.

Contribution

First detailed spectral and polarization imaging of Abell 2256 across 1-8 GHz, revealing complex filamentary structures and magnetic field variations.

Findings

Large Relic consists of filaments with correlated properties

Rotation Measure varies independently of other features

Detection of a connecting arc suggesting physical linkages

Abstract

We report new observations of Abell 2256 with the Karl G. Jansky Very Large Array (VLA) at frequencies between 1 and 8 GHz. These observations take advantage of the 2:1 bandwidths available for a single observation to study the spectral index, polarization and Rotation Measure as well as using the associated higher sensitivity to image total intensity features down to ~0.5" resolution. We find the Large Relic, which dominates the cluster, is made up of a complex of filaments which show correlated distributions in intensity, spectral index, and fractional polarization. The Rotation Measure varies across the face of the Large Relic but is not well correlated with the other properties of the source. The shape of individual filaments suggests that the Large Relic is at least 25 kpc thick. We detect a low surface brightness arc connecting the Large Relic to the Halo and other radio structures suggesting a physical connection between these features. The center of the F-complex is dominated by a very steep-spectrum, polarized, ring-like structure, F2, without an obvious optical identification, but the entire F-complex has interesting morphological similarities to the radio structure of NGC1265. Source C, the Long Tail, is unresolved in width near the galaxy core and is </~100pc in diameter there. This morphology suggests either that C is a one-sided jet or that the bending of the tails takes place very near the core, consistent with the parent galaxy having undergone extreme stripping. Overall it seems that many of the unusual phenomena can be understood in the context of Abell 2256 being near the pericenter of a slightly off-axis merger between a cluster and a smaller group. Given the lack of evidence for a strong shock associated with the Large Relic, other models should be considered, such as reconnection between two large-scale magnetic domains.