Spin evolution of long-period X-ray pulsars
  Spin evolution of X-ray pulsars in High Mass X-ray Binaries (HMXBs) is discussed under various assumptions about the geometry and physical parameters of the accretion flow. The torque applied to the neutron star from the accretion flow and equilibrium period of the pulsars are evaluated. We show that the observed spin evolution of the pulsars can be explained in terms of a scenario in which the neutron star accretes material from a magnetized stellar wind. 
N.R. Ikhsanov, Yu.S. Likh, and N.G. Beskrovnaya
astro-ph.HE