X-ray Pulsar

Neutron star with a powerful magnetic field in an X-ray binary. Gas accreted from the companion star is channeled to the magnetic poles
of the neutron star and forms X-ray emitting hot spots which move into and out of view as the neutron star spins, giving rise to regular X-ray pulses. The pulsation periods of X-ray pulsars range from 1.6 ms to >10 minutes in length. Long period X-ray pulsars have particularly strong magnetic fields that decrease their rotation rates through torques exerted on its magnetosphere.

Image source: http://lheawww.gsfc.nasa.gov/users/white/xrb/xrb.html.

Unlike radio pulsars, which are all spinning down due to energy losses in the form of relativistic particles and magnetic dipole radiation, some X-ray pulsars have been found to be spinning up; whereas, others have relatively stable spin rates or show erratic behavior (alternating periods of spin-up and spin-down). The variations in the spin rate arise because the pulsar can gain, lose or maintain its angular momentum depending on how the accreting material is transferred to the neutron star. They can have persistent mass transfer from Roche-lobe overflow, episodes of mass accretion (possibly due to an eccentric orbit that takes the neutron star close to the companion near periastron), or can be powered by stellar wind accretion. In contrast, a solitary radio
pulsar can only lose angular momentum through radiation of energy.