Gravitational light bending near neutron stars. II - Accreting pulsar spectra as a function of phase

We present X-ray pulse shapes and phase-dependent cyclotron spectra of simple accretion column and accretion cap models of rotating magnetized neutron stars, including general relativistic light-bending effects. We show that the latter effects can be strong, and discuss the beaming properties and phase-dependent spectral properties as a function of the stellar radius, using realistic magnetized input spectra. We show that a qualitatively correct fit to the observations of Her X-1 can be obtained only in two situations: either the accretion is of the cap (flat hot spot) type and the neutron star radius is larger than about 4 Schwarzschild radii, or else the accretion is of the column (protruding) type and the neutron star radius is of the order of 1.6 Schwarzschild radii. On the basis of various theoretical arguments and the current status of other evidence, the latter seems indicated at present.