A close binary lens revealed by the microlensing event Gaia20bof

TL;DR

This paper analyzes a microlensing event Gaia20bof, revealing a binary lens system through dense follow-up observations, with future data expected to resolve model degeneracies and better characterize the lensing system.

Contribution

It presents the first detailed analysis of Gaia20bof, demonstrating the effectiveness of automated follow-up in characterizing binary lenses in microlensing events.

Findings

Detected a binary lens anomaly in Gaia20bof

Spectroscopic data constrains source distance to ≤2.0 kpc

Future Gaia astrometry and imaging will resolve model degeneracies

Abstract

During the last 25 years, hundreds of binary stars and planets have been discovered towards the Galactic Bulge by microlensing surveys. Thanks to a new generation of large-sky surveys, it is now possible to regularly detect microlensing events across the entire sky. The OMEGA Key Projet at the Las Cumbres Observatory carries out automated follow-up observations of microlensing events alerted by these surveys with the aim of identifying and characterizing exoplanets as well as stellar remnants. In this study, we present the analysis of the binary lens event Gaia20bof. By automatically requesting additional observations, the OMEGA Key Project obtained dense time coverage of an anomaly near the peak of the event, allowing characterization of the lensing system. The observed anomaly in the lightcurve is due to a binary lens. However, several models can explain the observations. Spectroscopic observations indicate that the source is located at $\le2.0$ kpc, in agreement with the parallax measurements from Gaia. While the models are currently degenerate, future observations, especially the Gaia astrometric time series as well as high-resolution imaging, will provide extra constraints to distinguish between them.