SNR 0453-68.5: An Asymmetric Remnant and its Plerion in the Large Magellanic Cloud

TL;DR

This study analyzes the X-ray emission of SNR 0453-68.5 in the LMC, revealing a middle-aged composite remnant with a pulsar wind nebula, shaped by interactions with the surrounding ISM and reverse shock, with implications for supernova symmetry.

Contribution

It provides the first detailed X-ray analysis of this remnant, identifying the PWN and characterizing its spectral properties and interaction with the SNR environment.

Findings

The shell is dominated by shocked ISM, not ejecta.

The PWN has a photon index of 2.0, consistent across 0.4-1.2 pc.

No significant pulsar velocity transverse detected.

Abstract

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.