Toward Measuring the Microlensing Event Rate in the Galactic Center. I. Event Detection from the UKIRT Microlensing Survey Data

To overcome the high optical extinction, near-infrared (NIR) 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 NIR survey for the Nancy Grace Roman Space Telescope. Here, we analyze the online data from the UKIRT microlensing survey, reaching l = b = 0 degrees. 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 are higher than the optical event rates.