Hot Spots on Neutron Stars. II. The Observer's Sky

The gravitational lensing properties of neutron stars are explored, and the results are applied to X-ray emission from radio and X-ray binary pulsars. A simple method is described and illustrated for calculating the apparent brightness and appearance of the observer's sky for any model of emission from the stellar surface. The case where the emission arises solely from two antipodal hot spots is examined. It is found that for typical neutron star parameters the inclusion of gravitational effects makes it 3-10 times less likely, on average, that a given observer will see only one hot spot of the star, assuming no bias in the angle between the magnetic and spin axes. It is also shown that when relativistic effects are included, the modulation of the light curve arising from two antipodal hot spots is virtually independent of the size of the spots. Thus, unlike the flat space result, it is impossible to obtain arbitrary degrees of modulation by simply considering smaller emitting regions.