Gravitational excitation of high frequency QPOs

TL;DR

This paper explores how gravitational perturbations from neutron star asymmetries or companion stars could excite high-frequency QPOs in neutron-star binaries through resonant oscillations in the accretion disk.

Contribution

It proposes a mechanism involving gravitational excitation of disk oscillations by neutron star asymmetries or binary companions, offering a potential explanation for high-frequency QPOs.

Findings

Neutron-star asymmetries can induce significant radial and vertical oscillations.

Binary companions may produce notable radial but not vertical oscillations.

Neutron-star quadrupole moments could be large enough to excite these oscillations.

Abstract

We discuss the possibility that high-frequency QPOs in neutron-star binary systems may result from forced resonant oscillations of matter in the innermost parts of the accretion disc, excited by gravitational perturbations coming from asymmetries of the neutron star or from the companion star. We find that neutron-star asymmetries could, in principle, be effective for inducing both radial and vertical oscillations of relevant amplitude while the binary companion might possibly produce significant radial oscillations but not vertical ones. Misaligned neutron-star quadrupole moments of a size advocated elsewhere for explaining limiting neutron star periods could be large enough also for the present purpose.