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   72189
   We propose ASCA observations of four clusters of galaxies found to be
   among the most X-ray luminous clusters in the sky in the ROSAT All-Sky
   Survey as well as in deep HRI pointed observations. These systems form
   part of a statistical sample of massive clusters selected from RASS
   cluster samples for an in-depth study of the mass distribution in
   clusters by combining X-ray mass determinations with those from
   observations of strong gravitational lensing. For all targets proposed
   here for observation we have obtained deep CCD images from Mauna Kea.
   Our combined X-ray/lensing approach will provide the most accurate and
   reliable measurement of cluster masses for a statistical sample to date
   and will allow us to resolve the issue of discrepancies between X-ray
   and lensing mass determinations.
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