VLBA Measurement of the Transverse Velocity of the Magnetar XTE J1810−197

Abstract

We have obtained observations of the magnetar XTE J1810-197 with the Very Long Baseline Array (VLBA) at two epochs separated by 106 days, at wavelengths of 6 and 3.6 cm. Comparison of the positions yields a proper-motion value of 13.5 ± 1.0 mas yr-1 at an equatorial position angle of 209.4° ± 2.4° (east of north). This value is consistent with a lower significance proper-motion value derived from infrared observations of the source over the past 3 years, also reported here. Given its distance of 3.5 ± 0.5 kpc, the implied transverse velocity corrected to the local standard of rest is 212 ± 35 km s-1 (1 σ). The measured velocity is slightly below the average for normal young neutron stars, indicating that the mechanism(s) of magnetar birth need not lead to high neutron star velocities. We also use Australia Telescope Compact Array, Very Large Array, and these VLBA observations to set limits on any diffuse emission associated with the source on a variety of spatial scales, concluding that the radio emission from XTE J1810-197 is >96% pulsed.