Proper Motion of the High-Velocity Pulsar in SNR MSH 15-56

TL;DR

This study measures the proper motion of a pulsar in SNR MSH 15-56 using 15 years of Chandra X-ray data, constraining its velocity and direction, and models the remnant's evolution considering an ambient density gradient.

Contribution

It provides the first proper motion measurement of the pulsar in MSH 15-56 and links this to a hydrodynamical model explaining the remnant's asymmetric morphology.

Findings

Pulsar velocity of approximately 720 km/s.

Remnant morphology explained by an ambient density gradient.

Consistent SNR age estimate of around 11,000 years.

Abstract

We present a measurement of the proper motion of the presumed pulsar in the evolved composite supernova remnant (SNR) MSH 15-56 whose pulsar wind nebula (PWN) has been disrupted by the supernova (SN) reverse shock. Using Chandra X-ray observations acquired over a baseline of 15 years, we measure a pulsar velocity of 720 (+290/-215) km/s and a direction of motion of 14 +/- 22 degrees west of south. We use this measurement to constrain a hydrodynamical model for the evolution of this system and find that its morphology is well-described by an SNR expanding in an ambient density gradient that increases from east to west. The effect of the density gradient and the pulsar's motion is an asymmetric interaction between the SN reverse shock and the PWN that displaces the bulk of the PWN material away from the pulsar, towards the northeast. The simulation is consistent with an SNR age of 11,000 years, an SN ejecta mass of 10 solar masses, and an average surrounding density of 0.4 cm^-3. However, a combination of a higher SN ejecta mass and ambient density can produce a similar SNR morphology at a later age.