Understanding the Evolution of Composite SNRs: An XMM Study of MSH 15-56

MSH 1556 is the prototypical example of an evolved composite supernova remnant(SNR) consisting of a sweptup shell and a pulsar wind nebula (PWN) that appearsto be disrupted by the supernova (SN) reverse shock (RS). Gammaray emission isdetected at the position of the SNR that may be produced in the PWN/RSinteraction. We propose a 336 ks XMM observation of the entire SNR, crucial forcharacterizing the properties of the ambient medium, the SN ejecta, and the PWN,and for uncovering the origin of the highenergy emission. The analysis willallow us to test our hydrodynamical models for the evolution of composite SNRsand significantly advance our general understanding of the latephase structureand evolution of these systems. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]