Repeating microlensing events in the OGLE data

TL;DR

This study systematically searches for repeating microlensing events in OGLE data, identifying 19 candidates including 6 due to wide binary lenses, and highlights the potential for future wide-field surveys to enhance such detections.

Contribution

It provides the first large-scale search for repeating microlensing events in OGLE data, confirming theoretical predictions and identifying misclassified events.

Findings

19 repeating candidates found, 6 due to wide binary lenses

Approximately 2% of OGLE-III events are misclassified as microlensing

Future wide-field surveys will significantly increase the detection of repeating events

Abstract

Microlensing events are usually selected among single-peaked non-repeating light curves in order to avoid confusion with variable stars. However, a microlensing event may exhibit a second microlensing brightening episode when the source or/and the lens is a binary system. A careful analysis of these repeating events provides an independent way to study the statistics of wide binary stars and to detect extrasolar planets. Previous theoretical studies predicted that 0.5 - 2 % of events should repeat due to wide binary lenses. We present a systematic search for such events in about 4000 light curves of microlensing candidates detected by the Optical Gravitational Lensing Experiment (OGLE) towards the Galactic Bulge from 1992 to 2007. The search reveals a total of 19 repeating candidates, with 6 clearly due to a wide binary lens. As a by-product we find that 64 events (~2% of the total OGLE-III sample) have been miss-classified as microlensing; these miss-classified events are mostly nova or other types of eruptive stars. The number and importance of repeating events will increase considerably when the next-generation wide-field microlensing experiments become fully operational in the future.