Toward the Measurement of the Mass of Isolated Neutron Stars: Prediction of Future Astrometric Microlensing Events by Pulsars

Abstract

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 an NS will deviate from the expected nonlensed 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 identify two candidate events of stars involving lensing by a foreground pulsar in which the estimated light deflection of the background star will deviate from the nonlensed motion by more than 10 μas. PSR J185635−375435 passed ≅4.″1 from a 19.4 G magnitude star on J2014.9 with an estimated deflection of 13 μas, while PSR J084606−353340 may pass ∼0.″2 from a 19.0 G magnitude star on J2022.9 with an estimated deflection of 91 μas. However, the proper motion of the second event is highly uncertain. 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.