Wavelet analysis of MCG-6-30-15 and NGC 4051: a possible discovery of QPOs in 2:1 and 3:2 resonance

TL;DR

This study applies wavelet analysis to X-ray data from Seyfert galaxies MCG-6-30-15 and NGC 4051, revealing potential QPOs at specific frequencies that may connect AGN and X-ray binary phenomena.

Contribution

It demonstrates the effectiveness of wavelet transform in detecting QPOs in AGN, identifying resonant frequency ratios, and surpassing Fourier analysis in noise discrimination.

Findings

Detection of QPOs at ~2.5E-3 Hz and 4-6E-3 Hz

QPOs in 2:1 and 3:2 ratios suggest resonance phenomena

Wavelet analysis better isolates QPOs from noise than Fourier methods

Abstract

Following our previous work of Lachowicz & Czerny (2005), we explore further the application of the continuous wavelet transform to X-ray astronomical signals. Using the public archive of the XMM-Newton satellite, we analyze all available EPIC-pn observations for nearby Seyfert 1 galaxies MCG-6-30-15 and NGC 4051. We confine our analysis to 0.002-0.007 Hz frequency band in which, on the way of theoretically motivated premises, some quasi-periodic oscillations (QPOs) are expected to be found. We find that indeed wavelet power histogram analysis reveals such QPOs centered at two frequencies of ~2.5E-3 Hz and 4-6E-3 Hz, respectively. We show that these quasi-periodic features can be disentangled from the Poisson noise contamination level what is hardly to achieve with the standard Fourier analysis. Interestingly, we find some of them to be in 2:1 or 3:2 ratio. If real, our finding may be considered as a link between QPOs observed in AGN and kHz QPOs seen in X-ray binary systems.