Profiles and Polarization from Pulsar Magnetospheric Gaps

Only a handful of gamma-ray pulse profiles are available, but some characteristics are already clear. Gamma-ray emission occurs in 30-50% of the light curve, often with two distinct peaks, generally well separated from the radio pulsations. This implicates magnetospheric emission from well above the star surface, and several model geometries have been proposed to produce the pulses. We describe simulations of such models, with light curves computed in the vacuum (Deutsch field) approximation. GLAST should provide many more high quality light curves to match, but additional probes of the geometry are important. Polarization is, of course, an excellent probe but is only available at lower energies. High quality optical data measured for the Crab pulsar by Kanbach and colleagues present the most detailed challenge. We show that synchrotron emission from our magnetospheric model can reproduce many of the complex polarization features seen in these data. This match is quite constraining, requiring emission anisotropies linked to the geometry. Through dependence on pitch angle and self-absorption in the gaps, the model should also allow us to constrain the production of secondary pairs in the pulsar magnetosphere.