ROSAT/HRI study of the optically rich, lensing cluster CL0500-24
  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 $1.1^{+0.2}_{-0.1}\times10^{44}$ erg/s in the ROSAT band, the bolometric X-ray luminosity is $2.0^{+1.5}_{-0.7}\times 10^{44}$ 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 $(1.5\pm 0.8) \times 10^{14}$M$_\odot$, with an upper limit to the gas mass of about $0.5\times 10^{14}$M$_\odot$, corresponding to a gas mass fraction of $\le 30^{+30}_{-10}$\%. 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 $\Delta v \approx 3200$ km/s that happen to lie along the line of sight. 
Sabine Schindler, Joachim Wambsganss