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

Abstract In this paper, we conducted a search for the quasi-periodic oscillations (QPOs) in the hard X-ray (14–$195\:$keV) light curves of active galactic nuclei (AGNs). We retrieved monthly-binned light curve data from the 157-month Swift Burst Alert Telescope (BAT) catalog and focused on various types of AGNs, including a total of 1099 sources. The Jurkevich method, the Lomb–Scargle periodogram method, and the weighted wavelet Z-transform method were employed to search for the QPO. Based on these three methods, we found three promising candidates of AGNs with the QPO: NGC 2110 (SWIFT J0552.2$-$0727), Mkn 421 (SWIFT J1104.4$+$3812), and 3C 273 (SWIFT J1229.1$+$0202). Among them, NGC 2110 has a period of $\sim 1134~$d; Mkn 421 has a period of $\sim$642 d; and 3C 273 has a period of $\sim 367~$d. We discuss several physical mechanisms for the origin of the QPO, including the pulsational instabilities of the accretion disk, jet precession/rotation or helical structure, and supermassive binary black hole systems.