2005ApJ...635L..57L

We suggest a plausible interpretation for the twin kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries. We identify the upper kHz QPO frequencies to be the rotational frequency and the lower kHz QPOs as the standing kink modes of loop oscillations at the inner edge of the accretion disk, respectively. Taking into account the interaction between the neutron star magnetic field and the disk, this model naturally relates the twin QPO frequencies with the star's spin frequencies. We have applied the model to four X-ray sources with kHz QPOs detected simultaneously and the known spin frequencies.