Can disk-magnetosphere interaction models and beat frequency models for quasi-periodic oscillation in accreting X-ray pulsars be reconciled?

Aims: We review some aspects of the theory of magnetic threaded disks.
Methods: We discuss in particular the equations that determine the position of the inner disk boundary by using different prescriptions for the neutron star-accretion disk interaction. We apply the results to several accretion powered X-ray pulsars that show both quasi-periodic oscillations in their X-ray flux and spin-up/spin-down torque reversals. Under the hypothesis that the beat-frequency model is applicable to the quasi-periodic oscillations, we show that these sources provide an excellent opportunity to test models of the disk-magnetosphere interaction.
Results: A comparison is carried out between the magnetospheric radius obtained with all the prescriptions used in threaded disk models; this shows that none of those prescriptions is able to reproduce the combination of quasi-periodic oscillations and torque behaviour observed for different X-ray luminosity levels in the X-ray pulsars in the present sample.
Conclusions: This suggests that the problem of accretion disk threading by stellar magnetic field still lacks a comprehensive solution. We briefly discuss an outline of possible future developments in this field.