Microlensing Binaries Discovered through High-Magnification Channel

TL;DR

This study analyzes high-magnification microlensing events to investigate binary star distributions, highlighting degeneracies in binary solutions and identifying a potential brown-dwarf companion.

Contribution

First detailed analysis of binary microlensing events detected via high-magnification channel, examining degeneracies and binary parameter dependencies.

Findings

Degeneracy between close and wide binary solutions persists at 3σ confidence.

Degeneracy severity depends on binary separation and mass ratio.

Identified a strong brown-dwarf candidate with mass ratio ~0.1.

Abstract

Microlensing can provide a useful tool to probe binary distributions down to low-mass limits of binary companions. In this paper, we analyze the light curves of 8 binary lensing events detected through the channel of high-magnification events during the seasons from 2007 to 2010. The perturbations, which are confined near the peak of the light curves, can be easily distinguished from the central perturbations caused by planets. However, the degeneracy between close and wide binary solutions cannot be resolved with a $3\sigma$ confidence level for 3 events, implying that the degeneracy would be an important obstacle in studying binary distributions. The dependence of the degeneracy on the lensing parameters is consistent with a theoretic prediction that the degeneracy becomes severe as the binary separation and the mass ratio deviate from the values of resonant caustics. The measured mass ratio of the event OGLE-2008-BLG-510/MOA-2008-BLG-369 is $q\sim 0.1$, making the companion of the lens a strong brown-dwarf candidate.