Using wavelet analysis to study AGN x-ray variability

Abstract

In this work, we examine the application of the wavelet transform to the X-ray timing analyses of active galactic nuclei (AGN) and quasi-periodic eruption sources (QPEs). We find that the power spectral density (PSD) slope and the nature of the periodic signal can influence the ability to identify important features in the wavelet power spectrum. Several scenarios are simulated to test the effectiveness of the wavelet analysis to stationary and non-stationary data. We carried out a wavelet analysis to five unique objects: Ark 120, IRAS 13224-3809, RE J1034+396, the QPE GSN 069, and the eclipsing NGC 6814. The well-known quasi-periodic oscillation (QPO) in RE J1034+396 is significantly detected in the wavelet power spectrum. In IRAS 13224-3809, significant transient features appear during a flare at frequencies coincident with previously detected reverberation signals. The wavelet power spectrum of the QPE GSN 069 significantly reveals four persistent signals.