High-Frequency QPOs as a Product of Inner Disk Dynamics around Neutron Stars

TL;DR

This paper explores how the inner accretion disk dynamics around neutron stars produce high-frequency QPOs, linking observed frequencies to the neutron star's spin and disk flow characteristics.

Contribution

It introduces a model connecting the frequency difference of kHz QPOs to the neutron star's spin and inner disk flow regime, enhancing understanding of accretion physics.

Findings

Frequency difference relates to neutron star spin rate.

Sub-Keplerian or super-Keplerian flows influence QPOs.

Model explains observed QPO frequency variations.

Abstract

The kHz QPOs observed in a neutron star low mass X-ray binary are likely to be produced in the innermost regions of accretion disk around the neutron star. The rotational dynamics of the inner disk can be characterized by the presence of either sub-Keplerian or super-Keplerian accretion flow depending on the relative fastness of the neutron spin as compared to the Keplerian frequency at the inner disk radius. Within the magnetosphere-disk interaction model, the frequency difference between the two kHz QPOs observed in a given source can be estimated to be slightly higher than or nearly around the neutron star spin frequency if the neutron star is a slow rotator and less than the stellar spin frequency if the neutron star is a fast rotator.