  The quasi-periodic oscillations (QPOs) found in active galactic nuclei (AGNs)
are a very interesting observational phenomenon implying an unknown physical
mechanism around supermassive black holes. Several AGNs have been found to have
QPO phenomena in the X-ray energy band. Long-duration X-ray observations were
collected and reduced for six AGNs with a suspected QPO. The Gaussian process
(GP) model celerite was used to fit the light curves and to search for the
quasi-periodicity behavior. The power spectral density and parameter posterior
distributions of each light curve were calculated with the optimal model. Of
the six AGNs, only RE J1034+396 was found to have a QPO of about 3600 s. The
other five sources do not show QPO modulation behavior. We propose that a hot
spot on the accretion disk is a possible physical mechanism resulting in this
quasi-periodic behavior of AGNs.
