Hilbert-Huang Transform analysis of quasi-periodic oscillations in MAXI J1820+070

TL;DR

This study uses Hilbert-Huang transform to analyze low-frequency quasi-periodic oscillations in MAXI J1820+070, revealing phase lag behavior, frequency modulation, and potential links to jet physics.

Contribution

It applies the Hilbert-Huang transform to QPO analysis, providing new insights into phase lag, frequency modulation, and their physical origins in black hole binaries.

Findings

QPO phase lag is negative and energy-dependent

Frequency modulation causes QPO peak broadening

Modulations may originate from jet-related internal shocks

Abstract

We present time-frequency analysis, based on the Hilbert-Huang transform (HHT), of the evolution on the low-frequency quasi-periodic oscillations (LFQPOs) observed in the black hole X-ray binary MAXI J1820+070. Through the empirical mode decomposition (EMD) method, we decompose the light curve of the QPO component and measure its intrinsic phase lag between photons from different energy bands. We find that the QPO phase lag is negative (low energy photons lag behind high energy photons), meanwhile the absolute value of the lag increases with energy. By applying the Hilbert transform to the light curve of the QPO, we further extract the instantaneous frequency and amplitude of the QPO. Compared these results with those from the Fourier analysis, we find that the broadening of the QPO peak is mainly caused by the frequency modulation. Through further analysis, we find that these modulations could share a common physical origin with the broad-band noise, and can be well explained by the internal shock model of the jet.