SNR 0453-68.5: An Asymmetric Remnant and its Plerion in the Large   Magellanic Cloud
  We present a comprehensive study of the X-ray emission from SNR 0453-68.5 in the Large Magellanic Cloud (LMC) as seen from the \textit{Chandra} X-ray Observatory. This object is in a class of composite remnants that exhibit a shell of emission surrounding a central plerion, more commonly known as a pulsar wind nebula (PWN). This is one of only five remnants in the LMC with an identified PWN. We find that the shell of emission is not ejecta dominated, but rather due to shocked ISM that has been swept up by the supernova blast wave or located in a precursor cavity wall. This is supported by the morphology of the local molecular cloud as seen with the \textit{Spitzer} Space Telescope. The spectral properties are consistent with a middle-aged remnant $>$17000 years old. A point source detected within the central knot is determined to be the pulsar powering the synchrotron emission of the PWN. Spectral fits show the nebula is well characterized by a power law with photon index $\Gamma=2.0$. This index is constant over a spatial scale of 0.4-1.2 pc, which is inconsistent with younger PWN containing remnants such as the Crab Nebula and SNR 0540-69.3. These fits also contain significant contributions from an ejecta dominated thermal plasma which we interpret as evidence of mixing during an evolved interaction of the PWN with the reverse shock of the SNR. We observe no evidence that the central pulsar contains a significant velocity transverse to the line of sight and argue that despite the asymmetric surface brightness distribution the SN explosion giving birth to this remnant may have been quite symmetric. 
Randall L. McEntaffer, Thomas Brantseg, and Morgan Presley
astro-ph.HE