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

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 yr Chandra baseline. After correcting the observations’ astrometric solutions using reference Gaia stars’ positions, we measure a total proper motion of 24.7 ± 6.8 mas yr −1 at an angle of 336° ± 16° east of north. Using the distance estimates from the literature of 2.1 and 3.8 kpc, this proper motion corresponds to Galactic rotation-corrected transverse velocities of 264d 2.1 ± 79 km s −1 and 474d 3.8 ± 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.