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   72186
   We propose ASCA observations of two previously unknown galaxy clusters
   at z~0.3 found to be among the most X-ray luminous clusters in the sky.
   CL0142.9+4438 and CL1938.3+5409 were discovered in an ongoing X-ray
   survey in search of clusters behind the Galactic Plane. The detection
   of these exceptional systems and the overall success of the program
   demonstrate the potency of the X-ray approach and the need to push
   cluster surveys and large-scale structure studies well into the
   traditional zone of avoidance. Both clusters appear extremely rich and
   also exhibit signs of gravitational lensing. The proposed observations
   will allow us to measure the temperatures of these massive systems,
   enable determinations of their X-ray masses and allow a comparison of
   X-ray and lensing mass measurements.
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