ROSAT / HRI study of the optically rich , lensing cluster CL 0500 - 24

An analysis of a ROSAT/HRI observation of the optically rich, gravitationally lensing galaxy cluster CL0500-24 (or Abell S0506) is presented. We show that the X-ray luminosity of this supposedly rich cluster is relatively low at 1.1 −0.1 × 10 44 erg/s in the ROSAT band, the bolometric X-ray luminosity is 2.0 −0.7 × 10 44 erg/s. The X-ray emission is strongly correlated with the northern subconcentration of the cluster galaxies at redshift z = 0.327. The derived total mass of the (sub-)cluster within 1 Mpc is (1.5±0.8)×10M⊙, with an upper limit to the gas mass of about 0.5× 10M⊙, corresponding to a gas mass fraction of ≤ 30 −10%. The X-ray luminosity and the morphology of the extended X-ray emission supports the view that CL0500-24 consists of two clusters at a velocity difference of ∆v ≈ 3200 km/s that happen to lie along the line of sight.