Nonthermal Hard X-Ray Excess in the Coma Cluster: Resolving the Discrepancy between the Results of Different PDS Data Analyses

Abstract

The detection of a nonthermal excess in the Coma Cluster spectrum by two BeppoSAX observations analyzed with the XAS package (Fusco-Femiano et al.) has been disavowed by an analysis (Rossetti & Molendi) performed with a different software package (SAXDAS) for the extraction of the spectrum. To resolve this discrepancy we reanalyze the PDS data considering the same software used by Rossetti & Molendi. A correct selection of the data and the exclusion of contaminating sources in the background determination show that the SAXDAS analysis also reports a nonthermal excess with respect to the thermal emission at about the same confidence level of that obtained with the XAS package (?4.8 ?). In addition, we report the lack of the systematic errors investigated by Rossetti & Molendi and Nevalainen et al., taking into account the whole sample of the PDS observations off the Galactic plane, as already shown in our data analysis of Abell 2256 (Fusco-Femiano, Landi, & Orlandini). All this eliminates any ambiguity and confirms the presence of a hard tail in the spectrum of the Coma Cluster. ? 2007. The American Astronomical Society. All rights reserved.