Studying Two Massive Galaxy Clusters to be used as Gravitational Lens Telescopes

This is a proposal for reobservation of two clusters with highly flaredobservations from a systematic AO18 programme to study the most massive clustersat z 0.25 0.5 ideal candidates for gravitational lens telescopes whichhad no pointed Xray observations so far. A major goal is to characterise theirproperties for lensing studies and their use as gravitational lens telescopes.In addition these Xray observations complete an important volumelimited sampleof massive clusters to be used for a range of cosmological studies. Bothclusters with insufficient data show peculiar structure which makes their studyexciting on their own. To better resolve crucial structures in the clustercentres we also ask for Chandra exposures. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]