QPO frequency derivative - frequency correlation indicates non-Keplerian boundary layer with a maximum in rotation rate

TL;DR

This paper presents evidence that the frequency derivative and frequency correlation of kilohertz QPOs indicate a non-Keplerian boundary layer with a maximum rotation rate, supporting accretion disk models around neutron stars.

Contribution

It provides observational evidence for a non-Keplerian boundary layer with a maximum in rotation rate, supporting existing accretion disk theories.

Findings

Correlation between QPO frequency and its derivative indicates non-Keplerian rotation.

Observations support the boundary layer matching the Keplerian disk to the neutron star magnetosphere.

Strong evidence for a maximum in the boundary layer rotation rate.

Abstract

The correlation between the frequency and the absolute value of the frequency derivative of the kilohertz QPOs observed for the first time from 4U 1636-53 is a simple consequence and indicator of the existence of a non-Keplerian rotation rate in the accretion disk boundary layer. This paper interprets the observed correlation, showing that the observations provide strong evidence in support of the fundamental assumption of disk accretion models around slow rotators, that the boundary layer matches the Keplerian disk to the neutron star magnetosphere.