OGLE-2017-BLG-0039: Microlensing Event with Light from the Lens Identified from Mass Measurement

TL;DR

This paper analyzes a long-duration binary microlensing event, measuring the lens properties precisely and suggesting the lens is a bright binary star system at 6 kpc, enabling future confirmation through high-resolution imaging.

Contribution

The study precisely measures the microlens parallax and Einstein radius in a long-duration event, revealing the lens as a bright binary star system at 6 kpc, which is rare and allows for follow-up observations.

Findings

Microlens parallax measured as ~0.06 despite small value.

Angular Einstein radius determined as ~0.6 mas.

Lens identified as a binary with masses ~1.0 and 0.15 solar masses.

Abstract

We present the analysis of the caustic-crossing binary microlensing event OGLE-2017-BLG-0039. Thanks to the very long duration of the event, with an event time scale $t_{\rm E}\sim 130$ days, the microlens parallax is precisely measured despite its small value of $\pie\sim 0.06$. The analysis of the well-resolved caustic crossings during both the source star's entrance and exit of the caustic yields the angular Einstein radius $\thetae\sim 0.6$~mas. The measured $\pie$ and $\thetae$ indicate that the lens is a binary composed of two stars with masses $\sim 1.0~M_\odot$ and $\sim 0.15~M_\odot$, and it is located at a distance of $\sim 6$ kpc. From the color and brightness of the lens estimated from the determined lens mass and distance, it is expected that $\sim 2/3$ of the $I$-band blended flux comes from the lens. Therefore, the event is a rare case of a bright lens event for which high-resolution follow-up observations can confirm the nature of the lens.