A PARALLAX DISTANCE AND MASS ESTIMATE FOR THE TRANSITIONAL MILLISECOND PULSAR SYSTEM J1023+0038

The recently discovered transitional millisecond pulsar system J1023+0038 exposes a crucial evolutionary phase of recycled neutron stars for multiwavelength study. The system, comprising the neutron star itself, its stellar companion, and the surrounding medium, is visible across the electromagnetic spectrum from the radio to X-ray/gamma-ray regimes and offers insight into the recycling phase of millisecond pulsar evolution. Here, we report on multiple-epoch astrometric observations with the Very Long Baseline Array (VLBA) which give a system parallax of 0.731 ± 0.022 milliarcseconds (mas) and a proper motion of 17.98 ± 0.05 mas yr–1. By combining our results with previous optical observations, we are able to use the parallax distance of 1368+42–39 pc to estimate the mass of the pulsar to be 1.71 ± 0.16 M☉, and we are also able to measure the three-dimensional space velocity of the system to be 126 ± 5 km s–1. Despite the precise nature of the VLBA measurements, the remaining ∼3% distance uncertainty dominates the 0.16 M☉ error on our mass estimate.