Spacetime curvature, rotation and the pulse profile of fast pulsars

Abstract

Propagation of photons in the spacetime exterior to a rapidly rotating neutron star is investigated, using a rotationally perturbed spherical metric, to determine the pulse profile of fast pulsars. We find that spacetime curvature produces a substantial amount of divergence in the pulse beam width accompained be a reduction in the pulse intensity. Effects due to rotation are comparatively smaller, but rotation has the qualitatively important feature of producing a tilt of the pulse cone in the direction of rotation and a deformation of the cone. The asymmetry in the pulse profile so caused introduces a time delay in the arrival of photons emitted within the cone, which, in turn, affects the duty cycle of the pulsar.