Exploring Year-timescale Gamma-ray Quasi-Periodic Oscillations in Blazars: Evidence for Supermassive Binary Black Holes Scenario

TL;DR

This study analyzes 15 years of gamma-ray data from seven blazars, detecting quasi-periodic oscillations that suggest the presence of supermassive binary black holes and jet precession phenomena.

Contribution

It provides the first comprehensive statistical analysis of gamma-ray QPOs in blazars, linking observed periodicities to supermassive binary black hole models using MCMC constraints.

Findings

Detection of long-term and transient gamma-ray QPOs in seven blazars.

Statistical significance of QPOs confirmed with synthetic light curve simulations.

Constraints on jet parameters such as Lorentz factor and viewing angle in the binary black hole scenario.

Abstract

A comprehensive analysis of quasi-periodic oscillations (QPOs) in the gamma-ray emissions of blazars. Utilizing 15 years of Fermi-LAT observations of seven blazars in our sample, we identify both long-term and transient quasi-periodic oscillations in the gamma-ray light curves, with timescales ranging from a few months to years. These periodicities were detected using the Lomb-Scargle periodogram and REDFIT techniques. To robustly evaluate the statistical significance of the quasi-periodic signals observed in the Lomb-Scargle Periodograms, 30,000 synthetic $\gamma$-ray light curves were generated for each source using a stochastic model known as the Damped Random Walk (DRW) process. To investigate the physical origin of the observed gamma-ray QPOs with different timescales, we explore several plausible scenarios, with particular emphasis on a relativistic jet hosted by one of the black holes in a supermassive binary black hole system, jet precession, and helical motion of magnetized plasma blob within the jet. The $\gamma$-ray light curves exhibiting long-timescale quasi-periodic oscillations (QPOs) are analyzed within the framework of a supermassive binary black hole (SMBBH) model, employing a Markov Chain Monte Carlo (MCMC) approach, allowing us to constrain key physical parameters such as the jet Lorentz factor ($\Gamma$) and the viewing angle between the observer's line of sight ($\psi$) relative to the spin axis of SMBH.