This study aims to detect and characterize quasi-periodic oscillations (QPOs)
signals in X-ray observations of NGC 4151. We employed the Weighted Wavelet
Z-transform (WWZ) and Lomb-Scargle periodogram (LSP) methods for our analysis.
QPO signals with frequencies of 5.91 $\times 10^{-4}$ Hz and 5.68 $\times
10^{-4}$ 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
$\sigma$ and 3.3 $\sigma$, 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 $\sigma$, 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.

Cet article explore les excursions dans le temps et leurs implications.

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