Thermal and non-thermal emission from clusters Original Research Article

The first results of BeppoSAX on clusters of galaxies are presented. BeppoSAX offers broad-band spectroscopy in the 0.1–100 keV band with in addition imaging spectroscopy (arcminute resolution) in the 0.1–10 keV band. The high sensitivity and well-behaved point-spread function at high energies allows a study of the spatial distribution of both the iron Kα (6.7 keV) and Kβ (8 keV) complex. In the Perseus cluster the observed Kβ/Kα ratio is significantly higher than that predicted by standard thermal emission codes. This ratio decreases significantly outwards, providing evidence for resonance scattering of the iron Kα line. Taking this into account the iron abundance in the core of the Perseus cluster is nearly twice as large as previously thought. In A 2199 there is evidence for a hard non-thermal tail in the spectrum. Spatially resolved spectroscopy with the MECS instrument shows spectral hardening in the outer parts of the cluster. Moreover the simultaneously taken PDS spectrum of this cluster shows a tail extending up to at least 50 keV. Apart from the high-energy spectral component, the LECS data also show evidence for excess emission at large radii. The soft excess was also detected by the DS instrument of EUVE. This together is very suggestive for the presence of inverse Compton emission in A 2199. Recent EUVE and BeppoSAX observations of the Coma cluster also support the presence of strong non-thermal emission, in addition to the thermal component. We shorthly discuss a few consequences of these new results for the dynamics of clusters.