A regularly variable X-ray binary, in which the pulsation is associated with the spin period of the compact companion, a magnetized neutron star; abbr. XP. Periods range from a few seconds to a few minutes. These pulsations are thought to be caused by the magnetic field channelling the accreting gas on to the poles of the star, producing localized ‘hot spots’ which move in and out of view as the star spins. An example of such a system is Hercules X-1.