Near‐Field Microlensing from Wide‐Field Surveys

Abstract

We estimate the rate of near-field microlensing events expected from all-sky surveys and investigate the properties of the events. Under the assumption that lenses are composed of stars, our estimation of the event rate ranges from Γtot~0.1 yr-1 for a survey with a magnitude limit of Vlim=12 to Γtot~23 yr-1 for a survey with Vlim=18. We find that the average distances to the source star and lens vary considerably depending on the magnitude limit, while the dependencies of the event timescale and lens-source transverse speed are weak. We also find that the average lens-source proper motion of events expected from a survey with Vlim=18 would be ~40 mas yr-1, and the value further increases as the magnitude limit becomes lower, implying that the source and lens of a significant fraction of near-field events can be resolved from high-resolution follow-up observations conducted several years after the lensing magnification. From the investigation of the variation of the event characteristics depending on the position of the sky, we find that the average distances to source stars and lenses become shorter, the lens-source transverse speed increases, and the timescale becomes shorter as the Galactic latitude of the field increases. Because of the concentration of events near the Galactic plane, we find that >~50% of events would be detected in the field with b