Self-Trapping of Diskoseismic Corrugation Modes in Neutron Star Spacetimes

TL;DR

This paper investigates how higher-order multipole effects in rotating neutron star spacetimes influence disk oscillations, revealing conditions under which corrugation modes can become self-trapped, offering a potential observational probe of neutron star properties.

Contribution

It demonstrates that higher-order multipole moments can cause the Lense-Thirring frequency to turn over, enabling self-trapped c-modes in neutron star accretion disks, which was not previously known.

Findings

Self-trapped c-modes depend on high neutron star spin and quadrupole deformability.

Detection of these modes could constrain neutron star quadrupole moments.

The study links disk oscillation properties to neutron star equation of state.

Abstract

We examine the effects of higher-order multipole contributions of rotating neutron star (NS) spacetimes on the propagation of corrugation (c-)modes within a thin accretion disk. We find that the Lense-Thirring precession frequency, which determines the propagation region of the low-frequency fundamental corrugation modes, can experience a turnover allowing for c-modes to become self-trapped for sufficiently high dimensionless spin $j$ and quadrupole rotational deformability $\alpha$. If such self-trapping c-modes can be detected, e.g. through phase-resolved spectroscopy of the iron line for a high-spin low-mass accreting neutron star, this could potentially constrain the spin-induced NS quadrupole and the NS equation of state.