HOT CORONAE IN NEARBY RADIO GALAXIES

We present Rosat X-ray observations (with PSPC and HRI instruments) of a sample of radio galaxies belonging to the B2 catalog (3C31, 0206+35 , 1113+29 and 1553+24). The source 3C31 (B2 0104+32) belongs to the gr oup Arp 331 which shows emission from a diffuse hot intra-group gas an d from the brightest members of the group. We discuss both the morphol ogical and spectral features of this extended region deriving, in the framework of an isothermal beta model, the core radius, the central de nsity, the mass of the emitting material and gravitational mass, obtai ning indications on the presence of dark matter. A comparison of X-ray and radio data shows that the thermal pressure of the external gas ex ceeds the minimum pressure of the radio components, apart from the reg ion close to the nucleus where the jet is over-pressured. The X-ray em ission from the single members of the group and from the other galaxie s of the sample are consistent with a thermal spectrum originating fro m hot halos, which is a common feature in early type galaxies. We disc uss the main morphological and physical properties of these coronae. F urthermore, using also the data of previous works, we confirm the stro ng correlation between the X-ray and optical luminosities of all these galaxies.