  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.
