Soft (1 KEV) X-Ray Emission in Galaxy Clusters

Abstract

In this paper, we present results from our program of analysis of the broad band spectra of galaxy clusters. For two clusters, Abell 754 and IC 1262, we find evidence of a soft excess that can be modeled either as thermal emission or as non-thermal emission. For IC 1262, the thermal interpretation is nonphysical and the non-thermal model has further support from a radio halo that we propose exists in the cluster center. For Abell 754, we modeled the 1 keV thermal component as emission from the IGM of several galaxy groups that may lie within 300 kpc of the central region of the cluster. We further argue that this interpretation is more likely than either elliptical galaxies or intercluster gas as the origin of the emission. However, it is also possible that it is non-thermal in origin. Under the non-thermal interpretation, it is likely to originate from primary cosmic-rays accelerated at the shock front formed during the ongoing merger. Finally, we present the first observational L _nt versus T _x plot. The plot shows a weak (90%) correlation that indicates at least some of the non-thermal components detected in clusters must result from the formation of the cluster in order to provide this energy relationship.