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

The detection of a nonthermal excess in the Coma cluster spectrum by twoBeppoSAX observations analyzed with the XAS package (Fusco-Femiano et al.) hasbeen disavowed by an analysis (Rossetti & Molendi) performed with a differentsoftware package (SAXDAS) for the extraction of the spectrum. To resolve thisdiscrepancy we reanalyze the PDS data considering the same software used byRossetti & Molendi. A correct selection of the data and the exclusion ofcontaminating sources in the background determination show that also the SAXDASanalysis reports a nonthermal excess with respect to the thermal emission atabout the same confidence level of that obtained with the XAS package(~4.8sigma). Besides, we report the lack of the systematic errors investigatedby Rossetti & Molendi and Nevalainen et al. taking into account the wholesample of the PDS observations off the Galactic plane, as already shown in ourdata analysis of Abell 2256 (Fusco-Femiano, Landi & Orlandini). All thiseliminates any ambiguity and confirms the presence of a hard tail in thespectrum of the Coma cluster.Comment: 12 pages, 2 figures. Accepted for publication in ApJ Letter