Frequency Correlation of QPOs Based on a Resonantly-Excited Disk-Oscillation Model

TL;DR

This paper extends a disk-oscillation model to include low-frequency corrugation waves, explaining observed correlations between high- and low-frequency QPOs in neutron-star X-ray binaries.

Contribution

It introduces the excitation of low-frequency corrugation waves alongside inertial-acoustic oscillations in a resonant disk model, explaining QPO frequency correlations.

Findings

Model reproduces observed QPO correlations in Cir X-1

Incorporates low-frequency corrugation waves into the resonance model

Suggests specific neutron star parameters for matching observations

Abstract

In previous papers, we have proposed a model that the high-frequency quasi-periodic oscillations (HF QPOs) observed in black-hole and neutron-star X-ray binaries are inertial-acoustic oscillations that are resonantly excited on a one-armed deformed disk by nonlinear couplings between the oscillations and the disk deformation. In this paper we show that in addition to the inertial-acoustic waves, one-armed corrugation waves are also excited in the deformed disks. They are low-frequency oscillations. We examine frequencies and their correlations among the inertial-acoustic oscillations and the corrugation waves that are excited, in order to know whether they can describe observed frequency correlations among kHz QPOs and low-frequency QPOs (LF QPOs) in neutron-star X-ray binaries. The results seem to well describe the observed correlations in Cir X-1, if we adopt $M= 1.5\sim 2.0 M_\odot$ and $a_* \sim 0.8$, where $M$ is the mass of the central star and $a_*$ is the dimensionless spin parameter of the metric. Finally, assumptions involved in this disk-oscillation model are briefly summarized and discussed.