Binary Source Lensing and the Repeating OGLE EWS Events

TL;DR

This paper investigates the probability of observing repeating microlensing events caused by binary sources and lenses, comparing simulations with OGLE data to understand the binary nature of lenses and sources.

Contribution

The study presents detailed simulations of binary source lensing events and compares the probability of observing repeating events with real OGLE data, highlighting a discrepancy in binary fractions.

Findings

Simulated probability of second brightening: ~0.0018

Observed number of repeating events aligns with simulations if all lenses and sources are binary

Discrepancy suggests binary fraction may be overestimated or other factors involved

Abstract

A microlensing event may exhibit a second brightening when the source and/or the lens is a binary star. Previous study revealed 19 such repeating event candidates among 4120 investigated microlensing light curves of the Optical Gravitational Lensing Experiment (OGLE). The same study gave the probability ~ 0.0027 for a repeating event caused by a binary lens. We present the simulations of binary source lensing events and calculate the probability of observing a second brightening in the light curve. Applying to simulated light curves the same algorithm as was used in the analysis of real OGLE data, we find the probability ~ 0.0018 of observing a second brightening in a binary source lensing curve. The expected and measured numbers of repeating events are in agreement only if one postulates that all lenses and all sources are binary. Since the fraction of binaries is believed to be <= 50%, there seems to be a discrepancy.