Systematic Analysis of Quasi-Periodic Oscillation of Active Galactic Nuclei

📖 Project Description

Active galactic nuclei (AGNs) are believed to host supermassive black holes (SMBHs). Similar to those observed around stellar-mass BHs, the inner regions of their accretion disks may produce quasi-periodic oscillations (QPOs). However, QPOs have been confirmed in relatively few AGNs, possibly due to a lower intrinsic occurrence of detectable QPOs in SMBHs or limitations of current instruments. The first AGN discovered with QPO signals, RE J1034+396 is a narrow-line Seyfert 1 galaxy. It exhibits a highly variable QPO period that may also depend on energy. Since that discovery, roughly a dozen AGNs have been reported to show QPOs, with some observed across multiple epochs. In this project, we aim to investigate the non-stationary behavior of AGN QPOs using the stack-spectrum Hilbert-Huang transform (sHHT), an advanced time-frequency analysis method that has been used to track both gravitational wave signals and superorbital modulations in X-ray binaries. By applying sHHT to AGN QPOs, we will test its performance and gain insights into the underlying physics for these non-stationary signals.