Magnetic field and spin frequency of X-ray neutron star associated with the kHz QPOs

By means of the accretion induced magnetic field evolution model of neutron star in low mass X-ray binary, the star spin frequency evolution has been studied, and we find that the star spin frequency is almost independent of the mass accretion rate, initial magnetic field and initial period, when the star magnetosphere evolves less than about five star radii with the spin frequency of about 100 Hz. However, the similar distributions of kHz QPOs in the bright Z sources (∼Eddington accretion rate) and in the less luminous Atoll ones (∼1% Eddington accretion rate) imply that both sources share the similar magnetosphere radii and spin frequencies, which is consistent with our theoretical model.