Including the effect of gravitational light bending in X-ray profile modelling

Abstract

The purpose of this work is togeneralize pulse shape modelling to include the effect of light bendingdue to general relativity. A simple analytical formula is found todescribe the light-bending effect accurately, and is incorporatedinto the emission model for calculation of the pulse shapes fromrotating accreting neutron stars. Least-squares fittings are performedto a subset of pulsars studied by Leahy. The fittings with lightbending show significant improvement over the fittings without lightbending, and the resulting derived emission region geometry givesnarrower rings, as expected on theoretical grounds. The model is alsoapplied to the transient pulsar EXO 2030+375. The relation betweenthe luminosity and the properties of the emission rings is studied.For this pulsar we conclude that some effect other than changingemission ring size is responsible for the change in pulse shape.