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 }<SUB>{{E</SUB>}}. 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 }<SUB>{{E</SUB>}}. From the combination of the measured {π }<SUB>{{E</SUB>}} and {θ }<SUB>{{E</SUB>}}, 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 <SUB>1</SUB> = 0.18 ± 0.01 M <SUB>⊙</SUB> and M <SUB>2</SUB> = 0.16 ± 0.01 M <SUB>⊙</SUB> located at a distance {D}<SUB>{{L</SUB>}}=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<SUP>-1</SUP>, suggests that the lens can be directly observed from future high-resolution follow-up observations.