Towards the measurement of the mass of isolated neutron stars - Prediction of future astrometric microlensing events by pulsars

Abstract

The mass of single neutron stars (NSs) can be measured using astrometric microlensing events. In such events, the center-of-light motion of a star lensed by a NS will deviate from the expected non-lensed motion and this deviation can be used to measure the mass of the NS. I search for future conjunctions between pulsars, with measured proper motion, and stars in the GAIA-DR2 catalog. I identified one candidate event of a star that will possibly be lensed by a pulsar during the next ten years in which the expected light deflection of the background star will deviate from the non-lensed motion by more than 0.05 mas. Given the position and proper motion of PSR J0846-3533, it will possibly pass ~0.2" from a 19.0 G magnitude background star in 2022.9. Assuming a 1.4 solar mass NS, the expected maximum deviation of the background star images from the uniform-rate plus parallax motion will be 0.091 mas. This pulsar position has a relatively large uncertainty and therefore additional observations are required in order to verify this event. I briefly discuss the opposite case, in which a pulsar is being lensed by a star. Such events can be used to measure the stellar mass via pulsar timing measurements. I do not find good candidates for such events with predicted variations in the pulsar period derivative, divided by 1 s, exceeding 10^-20 s^-1. Since only about 10% of the known pulsars have measured proper motions, there is potential for an increase in the number of predicted pulsar lensing events.