Modelling pulse profiles with LOFT
As a neutron star rotates, emission from the hotspot generates a pulse profile. The energy-dependence of the pulse profile properties enables us to infer mass and radius. General relativistic effects such as gravitational lightbending (which leads to partial visibility of the back side of the star) and special relativistic Doppler effects combine to encode information about mass and radius in the pulse profile. The panel shows the pulse profile and the phase dependence of spectral colour for a neutron star spinning at 600 Hz. Spectral colour is the ratio of the number of photons with energies above to those below the blackbody temperature. Colour maximum occurs near the spot's line of sight approach velocity maximum, flux maximum near the spot's projected area maximum. The former thus precedes the latter. The dashed line shows the sinusoid that most closely describes the flux oscillations.