Supermodel Analysis of the Hard X-ray Excess in the Coma Cluster

The Supermodel (SM) provides an accurate description of the thermal contribution by the hot intracluster plasma which is crucial for the analysis of the hard excess. In this paper, the thermal emissivity in the Coma cluster is derived starting from the intracluster gas temperature and density profiles obtained by the SM analysis of X-ray observables: the XMM-Newton temperature profile and the ROSAT brightness distribution. The SM analysis of the BeppoSAX/Phoswich Detector System (PDS) hard X-ray (HXR) spectrum confirms our previous results, namely, an excess at the confidence level (c.l.) of ~4.8σ and a nonthermal (NT) flux of (1.30 ± 0.40) × 10^-11 erg cm^-2 erg cm^-1 in the energy range 20-80 keV. A recent joint XMM-Newton/Suzaku analysis reports an upper limit of ~6 × 10^-12 erg cm^-2 erg cm^-1 in the energy range 20-80 keV for the NT flux with an average gas temperature of 8.45 ± 0.06 keV and an excess of NT radiation at a c.l. above 4σ, without including systematic effects, for an average XMM-Newton temperature of 8.2 keV in the Suzaku/HXD-PIN FOV, in agreement with our earlier PDS analysis. Here we present a further evidence of the compatibility between the Suzaku and BeppoSAX spectra, obtained by our SM analysis of the PDS data, when the smaller size of the HXD-PIN FOV and the two different average temperatures derived by XMM-Newton and by the joint XMM-Newton/Suzaku analysis are taken into account. The consistency of the PDS and HXD-PIN spectra reaffirms the presence of an NT component in the HXR spectrum of the Coma cluster. The SM analysis of the PDS data reports an excess at c.l. above 4σ also for the higher average temperature of 8.45 keV thanks to the PDS FOV being considerably greater than the HXD-PIN FOV.