Quasi-periodic oscillations under wavelet microscope: the application of Matching Pursuit algorithm

TL;DR

This paper applies wavelet and Matching Pursuit algorithms to analyze low-frequency QPOs in black hole systems, revealing they are composed of independent oscillations likely excited by turbulence, challenging previous models.

Contribution

It introduces the use of Matching Pursuit for detailed time-frequency analysis of QPOs, providing new insights into their physical nature.

Findings

QPOs are made of multiple independent oscillations

Frequency remains constant over the oscillation lifetime

Supports turbulence-driven excitation models

Abstract

We zoom in on the internal structure of the low-frequency quasi-periodic oscillation (LF QPO) often observed in black hole binary systems to investigate the physical nature of the lack of coherence in this feature. We show the limitations of standard Fourier power spectral analysis for following the evolution of the QPO with time and instead use wavelet analysis and a new time-frequency technique -Matching Pursuit algorithm- to maximise the resolution with which we can follow the QPO behaviour. We use the LF QPO seen in a very high state of XTE J1550-564 to illustrate these techniques and show that the best description of the QPO is that it is composed of multiple independent oscillations with a distribution of lifetimes but with constant frequency over this duration. This rules out models where there is continual frequency modulation, such as multiple blobs spiralling inwards. Instead it favours models where the QPO is excited by random turbulence in the flow.