Detection of Periodic Variability in Simulated QSO Light Curves

TL;DR

This study assesses the likelihood of false detections of periodic signals in simulated quasar light curves, highlighting challenges in identifying binary black hole systems with upcoming large surveys like LSST.

Contribution

It demonstrates that false alarms are common in Lomb-Scargle analysis of simulated quasar light curves, emphasizing caution in future binary black hole claims from LSST data.

Findings

Thousands of false binary black hole candidates could be identified.

False alarms persist even with conservative false-alarm probability thresholds.

Caution is needed when interpreting periodic signals in large quasar surveys.

Abstract

Periodic light curve behavior predicted for some binary black hole systems might be detected in large samples, such as the multi-million quasar sample expected from the Large Synoptic Survey Telescope (LSST). We investigate the false-alarm probability for the discovery of a periodic signal in light curves simulated using damped random walk (DRW) model. This model provides a good description of observed light curves, and does not include periodic behavior. We used the Lomb-Scargle periodogram to search for a periodic signal in a million simulated light curves that properly sample the DRW parameter space, and the LSST cadence space. We find that even a very conservative threshold for the false-alarm probability still yields thousands of "good" binary black hole candidates. We conclude that the future claims for binary black holes based on Lomb-Scargle analysis of LSST light curves will have to be interpreted with caution.