Time delays, Doppler effects and oblateness: results for the ms pulsar SAXJ1808-3658

A method is presented for including the time‐delays, Doppler effects and oblateness of a rapidly rotating neutron star when fitting X‐ray light curves. Doppler effects and time‐delays are previously known to be essential. We find that the oblateness induced by rotation at frequencies above 300 Hz produces a geometric effect which needs to be accounted for when modelling light curves to extract constraints on the neutron star's mass and radius. The method is applied to model the light curves of the ms pulsar: SAXJ1808‐3658. The results of the modeling are discussed and the resulting constraints on mass and radius of the neutron stars.