OGLE-2016-BLG-0156: Microlensing Event With Pronounced Microlens-Parallax Effects Yielding 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 3 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 ${\pi }_{\mathrm{E}}$. 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 ${\theta }_{\mathrm{E}}$. From the combination of the measured ${\pi }_{\mathrm{E}}$ and ${\theta }_{\mathrm{E}}$, we determine the physical parameters of the lens. It is found that the lens is a binary composed of two M dwarfs with masses $M_1=0.18\pm 0.01M_{\odot }$ and $M_2=0.16\pm 0.01M_{\odot }$ located at a distance $D_{\rm L}= 1.35\pm 0.09
{\rm kpc}$. According to the estimated lens mass and distance, the flux from the lens comprises an important fraction, $\sim 25\mathrm{\%}$, of the blended flux. The bright nature of the lens combined with the high relative lens-source motion, $\mu =6.94\pm 0.50\mathrm{m}\mathrm{a}\mathrm{s}{\mathrm{y}\mathrm{r}}^{-1}$, suggests that the lens can be directly observed from future high-resolution follow-up observations.