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

TL;DR

This paper explores the potential of using astrometric microlensing by pulsars to measure the masses of isolated neutron stars, identifying a candidate event and discussing future prospects for such measurements.

Contribution

It presents a method to predict future pulsar-star conjunctions for measuring neutron star masses via astrometric microlensing, including a candidate event and analysis of related phenomena.

Findings

Identified a candidate microlensing event involving PSR J0846-3533 in 2022.

Estimated a maximum star image deviation of 0.091 mas for the candidate event.

Discussed the potential to measure stellar masses through pulsar lensing and the current limitations.

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.