Detection and characterization of quasiperiodic oscillations in the Seyfert galaxy NGC 4151

This study aims to detect and characterize quasiperiodic oscillations (QPOs) signals in x-ray observations of NGC 4151. We employed the weighted wavelet Z-transform and Lomb-Scargle periodogram methods for our analysis. QPO signals with frequencies of $5.91\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }\mathrm{Hz}$ and $5.68\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\text{ }\text{ }\mathrm{Hz}$ were detected in observations conducted by Chandra (ObsID 7830) in 2007 and XMM-Newton (ObsID 0761670301) in 2015, with confidence levels of $3.7\ensuremath{\sigma}$ and $3.3\ensuremath{\sigma}$, respectively. These signals are the first to be independently observed by two different telescopes over an eight-year period with closely matched frequencies. Most notably, the combined confidence level of the QPO signals from these two independent observations reaches an exceptional $5.2\ensuremath{\sigma}$, which is rare in astrophysical research and significantly strengthens our conviction in the authenticity of these signals. A detailed analysis of the observational data suggests that these QPO signals may be correlated with the properties of the central supermassive black hole. Additionally, spectral analysis of the observational data revealed no significant spectral differences between the QPO and non-QPO segments. These findings provide new insights into the x-ray variability mechanisms of the central black hole in NGC 4151 and offer a novel perspective for black hole mass estimation.