Probe the first shock generated in a major merger

We propose to observe the outskirt along the merger equator of a cluster pair 1E2216.00401 and 1E 2215.7 0404. This is a textbook premerger system, where aunique equatorial shock has been discovered using the recent XMMNewton andChandra observations proposed by the PI. We request a followup EPIC exposure of140 ks to accurately measure the entropy distribution along the equatorialregion to r200, and to search for other (earlier) equatorial shocks in thecluster outskirts. This observation will complete our view on the role played byequatorial shocks in energy transfer and circumcluster heating during thecluster formation. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]