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   61171
   ROSAT and ASCA observations found that groups of galaxires often
   contain large amount of X-ray hot gas, but their X-ray luminosities
   scatter widely in the range of 10e41-43 erg/s in spite of similar gas
   temperature. It is possible that groups of galaxies with low gas
   density are X-ray dark even if they contain as large amount of hot gas
   as X-ray bright groups. We propose to observe X-ray dark group of
   galaxy RGH101, in order to search very faint diffuse X-ray emission. If
   it is detected, it is suggested that most groups contain large amount
   of hot gas.
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