Is the 35 day cycle of her x-1 caused by the free precession of the neutron star?

It has been suggested that the 35 day clock mechanism of Her X-1 is caused by the precession of the neutron star. We made calculations for this model. Comparing our calculated results with observations we find:

1. (1) The theoretical light curve over the the 35 day cycle does not agree with the observed curve by Jones and Forman (1976).

2. (2) The change of pulse width and intensity with the 35 day phase is large in the model, seemingly disagreeing with the observations (e.g., Gruber et al. 1980).

3. (3) Parmer et al. (1985) reported that they did not see the expected 35 day variation in X-ray intensity expected in the model.

Pravdo et al. (1977) suggested that the observed X-ray pulses were formed by Thomson scattering of symmetric radiating beams generated near the surface of the neutron star. Our analysis based on the theory of Thomson scattering in strong magnetic fields shows that this model agrees well with the observations.