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 $\sim 10^5$ potentially-observable radio pulsars to be $\sim 0.2\mathrm{y}{\mathrm{r}}^{-1}$ for $10^{10}$ 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 $\sim 10\%$. 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 $\sim 15$ 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 $\sim 40\%$ of the events that last less than $\sim 10$ 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.

10 pages, accepted for publication in ApJ. v2 updated to reflect change of title in proof stage

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Cited by in corpus (2)

• PopSyCLE: A New Population Synthesis Code for Compact Object Microlensing Events
• Gaia pulsars and where to find them