Hard X-ray radiation has been detected for the first time in the Coma Cluster by BeppoSAX. Thanks to the unprecedented sensitivity of the Phoswich Detection System (PDS) instrument, the source has been detected up to similar to 80 keV. There is clear evidence (4.5 sigma) for nonthermal emission in excess of thermal emission above similar to 25 keV. The hard excess is very unlikely to be the result of X Comae, the Seyfert 1 galaxy that is present in the field of view of the PDS. A hard spectral tail that is due to inverse Compton scattering on cosmic microwave background photons is predicted in clusters, like Coma, with radio halos. Combining the present results with radio observations, a volume-averaged intracluster magnetic field of similar to 0.15 mu G is derived, while the electron energy density of the emitting electrons is similar to 7 x 10(-14) ergs cm(-3).
Fusco-Femiano R, Dal Fiume D, Feretti L, Giovannini G, Grandi P, Matt G, et al. (1999). Hard X-ray radiation in the Coma Cluster spectrum. THE ASTROPHYSICAL JOURNAL, 513(1), L21-L24.