OGLE-2015-BLG-0196: Ground-based Gravitational Microlens Parallax Confirmed By Space-Based Observation

TL;DR

This study confirms ground-based microlens parallax measurements with space-based observations for a binary lens event, enabling precise determination of the lens system's physical parameters.

Contribution

First confirmation of ground-based microlens parallax measurements using space-based data, improving accuracy of binary lens parameter estimation.

Findings

Binary lens consists of two similar-mass M dwarf stars.

Lens distance estimated at approximately 2.8 to 3.3 kpc.

Microlens parallax confirmed by Spitzer observations.

Abstract

In this paper, we present the analysis of the binary gravitational microlensing event OGLE-2015-BLG-0196. The event lasted for almost a year and the light curve exhibited significant deviations from the lensing model based on the rectilinear lens-source relative motion, enabling us to measure the microlens parallax. The ground-based microlens parallax is confirmed by the data obtained from space-based microlens observations using the {\it Spitzer} telescope. By additionally measuring the angular Einstein radius from the analysis of the resolved caustic crossing, the physical parameters of the lens are determined up to the two-fold degeneracy: $u_0<0$ and $u_0>0$ solutions caused by the well-known "ecliptic" degeneracy. It is found that the binary lens is composed of two M dwarf stars with similar masses $M_1=0.38\pm 0.04\ M_\odot$ ($0.50\pm 0.05\ M_\odot)$ and $M_2=0.38\pm 0.04\ M_\odot$ ($0.55\pm 0.06\ M_\odot$) and the distance to the lens is $D_{\rm L}=2.77\pm 0.23$ kpc ($3.30\pm 0.29$ kpc). Here the physical parameters out and in the parenthesis are for the $u_0<0$ and $u_0>0$ solutions, respectively.