Relativistic Effects and Polarization in Three High‐Energy Pulsar Models

Abstract

We present the influence of the special relativistic effects of aberration and light-travel time delay on pulsar high-energy light curves and polarization characteristics predicted by three models: the two-pole caustic model, the outer gap model, and the polar cap model. Position angle curves and degree of polarization are calculated for the models and compared with the optical data on the Crab pulsar. The relative positions of peaks in gamma-ray and radio light curves are discussed in detail for the models. We find that the two-pole caustic model can qualitatively reproduce the optical polarization characteristics of the Crab pulsar: fast swings of the position angle and minima in polarization degree, associated with both peaks. The anticorrelation between the observed flux and the polarization degree (observed in the optical band also for B0656+14) naturally results from the caustic nature of the peaks, which are produced in the model because of the superposition of radiation from many different altitudes, i.e., polarized at different angles. The two-pole caustic model also provides an acceptable interpretation of the main features in the Crab's radio profile. Neither the outer gap model nor the polar cap model is able to reproduce the optical polarization data on the Crab. Although the outer gap model is very successful in reproducing the relative positions of gamma-ray and radio peaks in pulse profiles, it can reproduce the high-energy light curves only when photon emission from regions very close to the light cylinder is included.