On twin peak quasi-periodic oscillations resulting from the interaction between discoseismic modes and turbulence in accretion discs around black holes

TL;DR

This paper explores how turbulence influences discoseismic modes in accretion disks around black holes, potentially explaining the twin peak QPO phenomena through a stochastic oscillator model that predicts observable frequency shifts.

Contribution

It introduces a toy model with stochastic frequency to demonstrate turbulence's role in generating twin peaks in QPOs, emphasizing turbulence's importance in disc oscillation dynamics.

Findings

Turbulence can induce 3:2 twin peaks in the oscillator spectrum.

Stochastic frequency acts as a separate driving agent for disc oscillations.

Turbulence significantly shifts the predicted oscillator frequencies.

Abstract

Given the peculiar and (in spite of many efforts) unexplained quasi-periodic oscillation (QPO) twin peak phenomena in accretion disc PSD observations, the present exploratory analytical article tries to inquire deeper into the relationship between discoseismic modes and the underlying driving turbulence in order to assess its importance. We employ a toy model in the form of a Gaussian white noise driven damped harmonic oscillator with stochastic frequency. This oscillator represents the discoseismic mode. (Stochastic damping was also considered, but interestingly found to be less relevant for the case at hand.) In the context of this model, we find that turbulence interacts with disc oscillations in interesting ways. In particular, the stochastic part in the oscillator frequency behaves as a separate driving agent. This gives rise to 3:2 twin peaks for some values of the physical parameters, which we find. We conclude with the suggestion that the study of turbulence be brought to the forefront of disc oscillation dynamics, as opposed to being a mere background feature. This change of perspective carries immediate observable consequences, such as considerably shifting the values of the (discoseismic) oscillator frequencies.