Search for quasi-periodic oscillations of AGNs in the Swift BAT 157-month hard X-ray survey.

This article focuses on the search for quasi-periodic oscillations (QPOs) in the hard X-ray (14–195 keV) light curves of active galactic nuclei (AGNs) using 157 months of data from the Swift Burst Alert Telescope (BAT) catalog. Analyzing 1099 AGNs with the Jurkevich method, Lomb–Scargle periodogram, and weighted wavelet Z-transform, the study identifies three promising QPO candidates: the Seyfert II galaxy NGC 2110 (~1134 days), the beamed AGN Mkn 421 (~642 days), and the quasar 3C 273 (~367 days). The authors discuss possible physical origins of these QPOs, including pulsational instabilities in accretion disks, jet precession or helical structures, and supermassive binary black hole systems (SMBBHS), with the orbital motion of SMBBHS favored for NGC 2110. The study emphasizes the need for multi-wavelength observations to confirm QPO detections and improve understanding of their origins in AGNs.