ar X iv : a st ro - p h / 99 01 01 8 v 1 4 J an 1 99 9 Hard X - ray Radiation in the Coma Cluster Spectrum

Hard X-ray radiation has been detected for the first time in the Coma cluster by Beppo-SAX . Thanks to the unprecedented sensitivity of the Phoswich Detection System (PDS) instrument, the source has been detected up to ∼80 keV. There is clear evidence (4.5σ) for non-thermal emission in excess of thermal above ∼25 keV. The hard excess is very unlikely due to X Comae, the Seyfert 1 galaxy present in the field of view of the PDS. A hard spectral tail due to inverse Compton on CMB photons is predicted in clusters, like Coma, with radio halos. Combining the present results with radio observations, a volume-averaged intracluster magnetic field of ∼ 0.15μG is derived, while the electron energy density of the emitting electrons is ∼ 7× 10−14 erg/cm3. Subject headings: cosmic microwave background — galaxies: clusters: individual (Coma) — magnetic fields — radiation mechanisms: non-thermal — X-rays: galaxies