088076

This is a proposal for reobservation of two clusters with highly flared observations from a systematic AO18 programme to study the most massive clusters at z = 0.25 - 0.5 - ideal candidates for gravitational lens telescopes - which had no pointed X-ray observations so far. A major goal is to characterise their properties for lensing studies and their use as gravitational lens telescopes. In addition these X-ray observations complete an important volume-limited sample of massive clusters to be used for a range of cosmological studies. Both clusters with insufficient data show peculiar structure which makes their study exciting on their own. To better resolve crucial structures in the cluster centres we also ask for Chandra exposures.