Towards Measuring Microlensing Event Rate in the Galactic Center: I. Events Detection from the UKIRT Microlensing Survey Data

Abstract

To overcome the high optical extinction, near-infrared observations are needed for probing the microlensing events toward the Galactic center. The 2015-2019 UKIRT microlensing survey toward the Galactic center is the first dedicated precursor near-infrared (NIR) survey for the Nancy Grace Roman Space Telescope. We here analyze the online data from the UKIRT microlensing survey, reaching $l=b=0^\circ$. Using the event-finder algorithm of KMTNet with the $\Delta \chi^2$ threshold of 250, we find 522 clear events, 436 possible events, and 27 possible anomalous events. We fit a point-source point-lens (PSPL) model to all the clear events and derive the PSPL parameters with uncertainties using a Markov chain Monte Carlo method. Assuming perfect detection efficiency, we compute the uncorrected event rates, which should serve as the lower limits on the true event rate. We find that the uncorrected NIR event rates are likely rising toward the Galactic center and higher than the optical event rates.