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   61190
   3C220.1 is a radio galaxy located at z=0.62, and revealed to have a
   "giant luminous arc". Such arcs are known to be images of background
   galaxies produced by the gravitational lensing effect. The arc radius
   of 3C220.1(= 9") implies "minimum" velocity dispersion of 720km/sec,
   which means that the lens potential is provided by a cluster of
   galaxies rather than a galaxy. Then it's very puzzling that the galaxy
   population of the fictitious cluster is apprerently very poor. We have
   analyzed the public archival data of ROSAT HRI to find an extended X-
   ray emission from the 3C220.1. We propose ASCA observations to
   determine the temperature and the redshift of the hot gas in the
   cluster. It will be a strong test to confirm the existence of deep
   cluster potentical well at z=0.62.
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