Research Of The Quasi-Period Variation Of γ-Ray Band Of Fermi Blazars

Blazars are a special subclass of active galactic nuclei,and their jets are almost aligned with the line of our sight,exhibiting multi-band variability on different timescales.They may display long-term quasi-periodic oscillations(QPOs)in the gamma-ray band.Therefore detecting QPO signals from blazars can help to study their radiation mechanisms and internal physical parameters.In this paper,we search for QPO signals in the gamma-ray band of blazars in Fermi-4FGL,and identify potential QPO candidates with periodic behavior.Chapter 1 provides an overview of active galactic nuclei and the significance of studying periodicity in blazars.Chapter 2 describes the observation and data processing of high-energy gamma-ray data.Chapter 3 discusses methods for detecting periodicity in unevenly sampled data,including the discrete correlation function method in the time domain and the Lomb-Scargle periodogram method in the frequency domain.To assess the reliability of the obtained QPO signals in the presence of noise,we simulate ten thousand light curves and estimate the significance of the QPO signals.In Chapter 4,we generate light curves for all Fermi-4FGL blazars from 2008 to 2022,and detect QPOs in the time domain.We identify 18 candidate blazars and perform QPO detection and significance analysis in the frequency domain.Four sources exhibit QPOs with a significance level of over 4σ,and J1333.0+3233seems to be previously unreported.We consider J1333.0+3233 to be a noise-dominated source,similar to OJ 014,and may exhibit better behavior with more observational data.We also identify several sources with lower significance.In Chapter 5,we discuss several models commonly used to explain QPO signals and analyze several high-significance sources.We believe that the origin of QPOs in blazars in the gamma-ray band is not caused by a single model,but perhaps by multiple mechanisms working together.