The diffuse soft excess emission in the Coma cluster from the ROSAT All-Sky Survey

TL;DR

This study analyzes ROSAT All-Sky Survey data to confirm and map the extensive soft X-ray excess around the Coma cluster, suggesting it originates from cosmic filaments either through non-thermal or thermal processes.

Contribution

It provides the first large-scale mapping of the soft excess in Coma using RASS data, confirming its extent and proposing a filamentary origin.

Findings

Soft X-ray excess extends up to 5 Mpc from Coma.

Detection of the largest soft excess halo to date.

Possible origin linked to cosmic filaments and accretion shocks.

Abstract

RASS data near the North Galactic Pole was analyzed in order to study the large-scale distribution of soft X-ray emission from the Coma cluster. These RASS data constitute the only available X-ray observations of Coma that feature an in situ -- temporally and spatially contiguous -- background, with unlimited and continuous radial coverage. These unique characteristics of the RASS data are used to deliver a final assessment on whether the soft excess previously detected in the Coma cluster is due to background subtraction errors, or not. This paper confirms the presence of soft X-ray excess associated with Coma, and reports the detection of 1/4 keV band excess out to 5 Mpc from the cluster center, the largest soft excess halo discovered to date. We propose that the emission is related to filaments that converge towards Coma, and generated either by non-thermal radiation caused by accretion shocks, or by thermal emission from the filaments themselves.