Galaxy Clusters in the Swift/BAT era II: 10 more Clusters detected above 15 keV

TL;DR

This paper reports the discovery of 10 new galaxy clusters in the Swift/BAT survey, analyzes their X-ray spectra, and investigates the presence of non-thermal hard X-ray excess, confirming thermal origins for most clusters.

Contribution

It presents 10 newly detected galaxy clusters in the hard X-ray band and provides detailed spectral analysis, including evidence for non-thermal emission in two clusters.

Findings

Most clusters' emission explained by thermal models

Evidence for non-thermal X-ray excess in Bullet and Abell 3667

Hard X-ray emission in clusters is generally thermal, except Bullet

Abstract

We report on the discovery of 10 additional galaxy clusters detected in the ongoing Swift/BAT all-sky survey. Among the newly BAT-discovered clusters there are: Bullet, Abell 85, Norma, and PKS 0745-19. Norma is the only cluster, among those presented here, which is resolved by BAT. For all the clusters we perform a detailed spectral analysis using XMM-Newton and Swift/BAT data to investigate the presence of a hard (non-thermal) X-ray excess. We find that in most cases the clusters' emission in the 0.3-200keV band can be explained by a multi-temperature thermal model confirming our previous results. For two clusters (Bullet and Abell 3667) we find evidence for the presence of a hard X-ray excess. In the case of the Bullet cluster, our analysis confirms the presence of a non-thermal, power-law like, component with a 20-100 keV flux of 3.4 \times 10-12 erg cm-2 s-1 as detected in previous studies. For Abell 3667 the excess emission can be successfully modeled as a hot component (kT=~13keV). We thus conclude that the hard X-ray emission from galaxy clusters (except the Bullet) has most likely thermal origin.