Proper Motion of the Neutron Star in the Supernova Remnant G18.9-1.1

TL;DR

This study measures the proper motion of a neutron star in supernova remnant G18.9-1.1 over 15 years, revealing its velocity and supporting the idea that neutron star kicks result from momentum conservation with ejecta.

Contribution

First direct measurement of the neutron star's proper motion in G18.9-1.1 using a 15-year Chandra baseline, providing new insights into neutron star velocities and supernova remnant dynamics.

Findings

Proper motion of 24.7 ± 6.8 mas/yr measured.

Transverse velocity estimated between 264 and 474 km/s.

Neutron star's motion opposes ejecta movement, supporting momentum conservation models.

Abstract

In this paper, we present the first direct measurement of the proper motion of the neutron star (NS) in the supernova remnant (SNR) G18.9-1.1 using a 15-year Chandra baseline. After correcting the observations' astrometric solutions using reference Gaia stars' positions, we measure a total proper motion of 24.7 $\pm$ 6.8 mas yr$^{-1}$ at an angle of $336^\circ \pm$ 16$^\circ$ east of north. Using the distance estimates from literature of 2.1 kpc and 3.8 kpc, this proper motion corresponds to Galactic rotation-corrected transverse velocities of 264d$_{2.1}$ $\pm$ 79 km s$^{-1}$ and 474d$_{3.8}$ $\pm$ 129 km s$^{-1}$, respectively. Our power ratio method analysis of SNR ejecta slightly favors the higher velocity, as multipole moments calculated from the back-evolved center using the farther distance are more consistent with values from other CCSNRs. The NS's motion is directly opposite the motion of bulk ejecta in G18.9$-$1.1, providing yet more evidence that NS kicks are generated via a conservation of momentum-like process between the NS and the ejecta, as has been observed in other SNRs.