X-ray observations of the Crushed Pulsar Wind Nebula and Rapidly Moving Pulsar in SNR MSH 15-56

Composite supernova remnants (SNRs) are those consisting of both a central pulsar that produces a wind of synchrotron-emitting relativistic particle and a supernova (SN) blast wave that expands into the surrounding interstellar medium (ISM). The evolution of the pulsar wind nebula (PWN) is coupled to the evolution of its host SNR and characterized by distinct stages, from the PWN’s early expansion into the unshocked SN ejecta to its late-phase interaction with the SNR reverse shock. The signatures of this PWN/SNR interaction can reveal important information about the SNR and PWN dynamics, the ambient medium, particle injection and loss processes, and the eventual escape of PWN’s energetic particles into the interstellar medium. I will present the analysis of recent X-ray observations of the evolved composite SNR MSH 15-56 that appears to have undergone an asymmetric interaction with the SN reverse shock. Such an asymmetric interaction can occur as a result of a density gradient in the ambient medium and/or a moving pulsar that displaces the PWN from the center of the SNR. The 15-year baseline of the Chandra observations allowed us to measure the proper motion of the pulsar, which indeed shows that it is moving at a high velocity. This analysis provides new insight into the evolution of this complex SNR and the late-phase evolution of composite SNRs in general.