OGLE-2016-BLG-0156: Microlensing Event with Pronounced Microlens-parallax Effects Yielding a Precise Lens Mass Measurement

We analyze the gravitational binary-lensing event OGLE-2016-BLG-0156, for which the lensing light curve displays pronounced deviations induced by microlens-parallax effects. The light curve exhibits three distinctive widely separated peaks and we find that the multiple-peak feature provides a very tight constraint on the microlens-parallax effect, enabling us to precisely measure the microlens parallax π_E. All the peaks are densely and continuously covered from high-cadence survey observations using globally located telescopes and the analysis of the peaks leads to the precise measurement of the angular Einstein radius θ_E. From the combination of the measured π_E and θ_E, we determine the physical parameters of the lens. It is found that the lens is a binary composed of two M dwarfs with masses M_1 = 0.18 ± 0.01 M⊙ and M_2 = 0.16 ± 0.01 M⊙ located at a distance D_L = 1.35 ± 0.09 kpc. According to the estimated lens mass and distance, the flux from the lens comprises an important fraction, ~25%, of the blended flux. The bright nature of the lens combined with the high relative lens-source motion, μ = 6.94 ± 0.50 mas yr^(−1), suggests that the lens can be directly observed from future high-resolution follow-up observations.