1997A&A...322...66S

An analysis of a ROSAT/HRI observation of the optically rich, gravitationally lensing galaxy cluster Cl 0500-24 (or Abell S0506) is presented. The X-ray luminosity and the morphology of the extended X-ray emission support the view that Cl 0500-24 consists of two subclusters at a velocity difference of {DELTA}v≃3200km/s that happen to lie along the line of sight and are probably physically unrelated. The X-ray emission is mainly correlated with one of the subclusters - the 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^+0.6_–0.4x10⁴⁴erg/s in the ROSAT band (5.6^+4.2_–2.0x10⁴⁴erg/s bolometric) indicating that there is no tight correlation between X-ray luminosity and optical richness. The derived total mass of the cluster of (1.5±0.8)x10¹⁴M_☉ (within 1Mpc of the X-ray maximum) is very low even when assigning it only to one subcluster. The gas mass within the same radius is 0.5x10¹⁴M_☉, corresponding to a high gas mass fraction of 30⁺³⁰_–10%.