Quasars with Periodic Variability: Capabilities and Limitations of Bayesian Searches for Supermassive Black Hole Binaries in Time-Domain Surveys

TL;DR

This study evaluates Bayesian methods for detecting supermassive black hole binaries via quasar periodicity, highlighting their capabilities and limitations using simulations modeled after current and upcoming sky surveys.

Contribution

The paper introduces a comprehensive simulation framework to assess Bayesian search techniques for SMBHBs in quasar light curves, considering realistic noise and survey conditions.

Findings

Shorter periods and larger amplitudes improve detection rates.

False positives are minimized in high-quality LSST-like data.

Detection rates are similar across CRTS and LSST simulations.

Abstract

Supermassive black hole binaries (SMBHBs) are an inevitable consequence of galaxy mergers. At subparsec separations, they are practically impossible to resolve, and the most promising technique is to search for quasars with periodic variability. However, searches for quasar periodicity in time-domain data are challenging due to the stochastic variability of quasars. In this paper, we used Bayesian methods to disentangle periodic SMBHB signals from intrinsic damped random walk (DRW) variability in active galactic nuclei light curves. We simulated a wide variety of realistic DRW and DRW+sine light curves. Their observed properties are modeled after the Catalina Real-time Transient Survey (CRTS) and expected properties of the upcoming Legacy Survey of Space and Time (LSST) from the Vera C. Rubin Observatory. Through a careful analysis of parameter estimation and Bayesian model selection, we investigated the range of parameter space for which binary systems can be detected. We also examined which DRW signals can mimic periodicity and be falsely classified as binary candidates. We found that periodic signals are more easily detectable if the period is short or the amplitude of the signal is large compared to the contribution of the DRW noise. We saw similar detection rates both in the CRTS and LSST-like simulations, while the false-detection rate depends on the quality of the data and is minimal in LSST. Our idealized simulations provide an excellent way to uncover the intrinsic limitations in quasar periodicity searches and set the stage for future searches for SMBHBs.