Resonant Excitation of Disk Oscillations in Two-Armed-Deformed Disks and Application to High-Frequency QPOs

TL;DR

This paper explores how vertical resonance in two-armed deformed disks can excite p-mode and g-mode oscillations, potentially explaining the observed time variation of high-frequency QPOs in low mass X-ray binaries.

Contribution

It introduces a new mechanism involving vertical resonance in two-armed disks for exciting oscillations, expanding previous models focused on horizontal resonance.

Findings

Vertical resonance excites disk oscillations in two-armed deformed disks.

Oscillation frequencies can vary over time with changes in disk structure.

Application to observed kHz QPOs suggests a possible explanation for their variability.

Abstract

In previous papers we showed that in a one-armed deformed disks, p-mode and g-mode oscillations are resonantly excited by horizontal resonance, and applied it to high frequency QPOs observed in low mass X-ray binaries. In that model, the observed time variation of kHz QPOs is regarded as a result of a time-dependent precession of the deformation. In this paper we consider another possible cause of time variation of kHz QPOs. That is, we demonstrate that in a two-armed deformed disks, p-mode and g-mode oscillations are excited by {\it vertical resonance}, not by horizontal resonance(horizontal resonance dampens them). Furthermore, we show that in the case of vertical resonance, the frequencies of disk oscillations excited can vary with time if vertical disk structure changes with time. A brief application of these results to the time variation of observed kHz QPOs is made.