Periodic Signals in Binary Microlensing Events

TL;DR

This paper introduces a modified Lomb-Scargle periodogram method to detect orbital periods in binary microlensing events, especially when the orbital motion causes quasi-periodic features in the light curves, despite complicating factors.

Contribution

It presents a novel modification of the Lomb-Scargle periodogram to accurately extract binary orbital periods from microlensing light curves with orbital motion effects.

Findings

Successfully extracts orbital periods from simulated binary lens events

Demonstrates method's effectiveness across different binary configurations

Enhances understanding of binary lens systems through periodicity analysis

Abstract

Gravitational microlensing events are powerful tools for the study of stellar populations. In particular, they can be used to discover and study a variety of binary systems. A large number of binary lenses have already been found through microlensing surveys and a few of these systems show strong evidence of orbital motion on the timescale of the lensing event. We expect that more binary lenses of this kind will be detected in the future. For binaries whose orbital period is comparable to the event duration, the orbital motion can cause the lensing signal to deviate drastically from that of a static binary lens. The most striking property of such light curves is the presence of quasi- periodic features, which are produced as the source traverses the same regions in the rotating lens plane. These repeating features contain information about the orbital period of the lens. If this period can be extracted, then much can be learned about the lensing system even without performing time-consuming, detailed light curve modeling. However, the relative transverse motion between the source and the lens significantly complicates the problem of period extraction. To resolve this difficulty, we present a modification of the standard Lomb-Scargle periodogram analysis. We test our method for four representative binary lens systems and demonstrate its efficiency in correctly extracting binary orbital periods.