Gravitational Microlensing by Neutron Stars and Radio Pulsars: Event Rates, Timescale Distributions, and Mass Measurements
Abstract
We investigate properties of Galactic microlensing events in which a stellar object is lensed by a neutron star. For an all-sky photometric microlensing survey, we determine the number of lensing events caused by 105 potentially-observable radio pulsars to be 0.2\ yr-1 for 1010 background stellar sources. We expect a few detectable events per year for the same number of background sources from an astrometric microlensing survey. We show that such a study could lead to precise measurements of radio pulsar masses. For instance, if a pulsar distance could be constrained through radio observations, then its mass would be determined with a precision of 10\%. We also investigate the time-scale distributions for neutron star events, finding that they are much shorter than had been previously thought. For photometric events towards the Galactic centre that last 15 days, around 7\% will have a neutron star lens. This fraction drops rapidly for longer time-scales. Away from the bulge region we find that neutron stars will contribute 40\% of the events that last less than 10 days. These results are in contrast to earlier work which found that the maximum fraction of neutron star events would occur on time-scales of hundreds of days.