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    PR # 31556                                                                   
     The study of gravitational lenses in clusters can provide very import       
     ant information on the gravitational mass distribution in clusters. F       
     or the analysis of the optical data, knowledge of the properties of t       
     he lens is required.  We propose to observe a cluster where two brigh       
     t arcs were discovered recently in follow-up observations of clusters       
      detected in the ROSAT All Sky Survey. The detected arcs fall into th       
     e category of the very luminous, giant arcs, which are very rare. The       
      geometry of the arcs is also very special, because they lie almost o       
     pposite to each other with respect to the cluster centre, which is ve       
     ry advantageous for a mass determination. Additionally, the X-ray bri       
     ghtness of the distant cluster is exceptional and makes it an ideal c       
    andidate for an X-ray observat                                               
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