We have used Polar Cap (PC) model simulations of γ-ray pulsars to derive light curves and spectra for Nearly Aligned Rotators (NARs), as well as a more general class of Single Polar Cap (SPC) models which do not require that the inclination α<<1. In these models the observed γ-rays are due to emission concentrated around the rim of a single PC, and may exhibit either one or two peaks. The interpeak emission seen in several doubly peaked sources is produced above the PC interior. If α~θ_b_, the half-width of the PC γ-beam, the peak-to-peak phase separation can be as large as ~0.4-0.5. Our simulation assumes the physics of conventional PC models, in which the γ-rays emerge from photon-pair cascades initiated by curvature radiation from accelerated PC electrons. Here we also assume that the acceleration extends up to heights of several radii above the neutron star surface. We find that the combined effects of increased PC radii (by factors >2) and extended acceleration zones solve a major problem with earlier PC models, namely their small beam widths which imply low detection probabilities. We compare our results with observations of the Vela pulsar, for models in which the primary electrons have a uniform surface density over the PC interior with a sharp increase (~3) near the rim. We describe model parameters which reproduce key features of both the Vela light curves and phase-resolved spectra.
Astronomy and Astrophysics Supplement Series
- Pub Date:
- November 1996
- GAMMA RAYS: THEORY;
- PULSARS: GENERAL;
- PULSARS: INDIVIDUAL: PSR 0833-45