Brown-dwarf companions in microlensing binaries detected during the 2016--2018 seasons

TL;DR

This study analyzes microlensing survey data from 2016-2018 to identify binary systems with brown-dwarf companions, using modeling and Bayesian mass estimation, resulting in six candidate systems with high probabilities of hosting brown-dwarf companions.

Contribution

First identification of brown-dwarf companions in microlensing binaries during 2016-2018, using anomaly modeling and Bayesian analysis to estimate companion masses.

Findings

Six candidate brown-dwarf binary systems identified.

High probability (>80%) of brown-dwarf companions in four systems.

Bayesian mass estimation effectively distinguishes brown-dwarf companions.

Abstract

With the aim of finding microlensing binaries containing brown-dwarf (BD) companions, we investigate the microlensing survey data collected during the 2016--2018 seasons. For this purpose, we first conducted modeling of lensing events with light curves exhibiting anomaly features that are likely to be produced by binary lenses. We then sorted out BD-companion binary-lens events by applying the criterion that the companion-to-primary mass ratio is $q \lesssim 0.1$. From this procedure, we identify 6 binaries with candidate BD companions, including OGLE-2016-BLG-0890L, MOA-2017-BLG-477L, OGLE-2017-BLG-0614L, KMT-2018-BLG-0357L, OGLE-2018-BLG-1489L, and OGLE-2018-BLG-0360L. We estimate the masses of the binary companions by conducting Bayesian analyses using the observables of the individual lensing events. According to the Bayesian estimation of the lens masses, the probabilities for the lens companions of the events OGLE-2016-BLG-0890, OGLE-2017-BLG-0614, OGLE-2018-BLG-1489, and OGLE-2018-BLG-0360 to be in the BD mass regime are very high with $P_{\rm BD}> 80\%$. For MOA-2017-BLG-477 and KMT-2018-BLG-0357, the probabilities are relatively low with $P_{\rm BD}=61\%$ and 69\%, respectively.