ROSAT HRI STUDY OF THE OPTICALLY RICH, LENSING CLUSTER CI0500-24/

An analysis of a ROSAT/HRI observation of the optically rich, gravitat ionally lensing galaxy cluster Cl 0500-24 (or Abell S0506) is presente d. The X-ray luminosity and the morphology of the extended X-ray emiss ion support the view that Cl 0500-24 consists of two subclusters at a velocity difference of Delta v approximate to 3200 km/s that happen to lie along the line of sight and are probably physically unrelated. Th e X-ray emission is mainly correlated with one of the subclusters - th e northern subconcentration at redshift z = 0.327. We show that the X- ray luminosity of this supposedly rich cluster is relatively low at 3. 1(-0.4)(+0.6) x 10(44) erg/s in the ROSAT band (5.6(-2.0)(+4.2) x 10(4 4) erg/s bolometric) indicating that there is no tight correlation bet ween X-ray luminosity and optical richness. The derived total mass of the cluster of (1.5 +/- 0.8) x 10(14) M. (within 1 Mpc of the X-ray ma ximum) is very low even when assigning it only to one subcluster. The gas mass within the same radius is 0.5 x 10(14) M., corresponding to a high gas mass fraction of 30(-10)(+30) %.