Asymmetric X-ray pulsar beam emission.

Many of the X-ray pulsars for which X-ray light curves have been presented in the literature exhibit asymmetric emission beams. The authors postulate the existence of an off-centre magnetic dipole field embedded in the rotating neutron star and show that such a field leads to varying rates of matter transfer between an accretion disc and the neutron star surface, over a rotation period. Assuming that the accretion rate onto the surface is simply related to the luminosity, it is shown that most of the observed asymmetries can be accounted for by this mechanism.