Magnetar counterparts, kinematics and birth sites with HST and JWST

TL;DR

This study uses HST and JWST imaging to identify magnetar counterparts, measure their proper motions, and investigate their birth sites, revealing insights into their kinematics, origins, and potential differences from other neutron stars.

Contribution

It provides new identifications of magnetar counterparts and analyzes their proper motions and birth sites, suggesting similarities with the broader neutron star population and hinting at a possible velocity difference.

Findings

Magnetar proper motions are marginally inconsistent with young pulsars.

Most magnetars have identified candidate birth sites.

Evidence suggests a possible dearth of high-velocity magnetars.

Abstract

Magnetars are highly magnetised, isolated neutron stars with uncertain formation channels. They comprise a potentially significant fraction of the young neutron star population in the Milky Way, and are implicated in the explosion mechanisms of some of the most powerful explosions in nature. We aim to identify magnetars in the near-infrared with Hubble Space Telescope (HST) and James Webb Space Telescope (JWST) imaging, in order to measure their proper motions and search for their birth sites. Candidate infrared counterparts are selected based on variability, colours and proper motions which are outliers with respect to other sources in the field. Precise proper motions are obtained by tying HST/WCF3 and JWST/NIRcam images to the Gaia reference frame. We newly identify counterpart candidates for PSRJ1622-4950, 1RXSJ 170849.0-400910 and CXOUJ164710.2-455216. The past trajectory of the 1RXSJ 170849.0-400910-associated source coincides with the supernova remnant G346.6-0.2. The transverse velocity distribution of magnetars is found to be marginally inconsistent with young pulsars, due primarily to a dearth of high velocity magnetars. A candidate birth site is identified inside the cone of possible past trajectories in nearly every case. We show, based on the inferred kinematic ages, that characteristic ages may frequently be lower than the true age, but caution that this depends on the reliability of the birth site associations. We conclude that magnetars are similar in terms of their kinematics and birth sites to the wider Galactic neutron star population, consistent with magnetar formation being a common outcome of massive star core-collapse. However, tentative evidence for a dearth of high-velocity magnetars is emerging. If real, this may arise from physical differences in the progenitor population giving rise to magnetars, or from differences in their post-formation velocity evolution.