High energy emission from pulsars: Outer gap scenario

I will give a brief review of the recent development in the emission models of isolated, rapidly rotating neutron stars, focusing on the gamma-ray radiation mechanism in their outer magnetospheres. By examining the Poisson equation for the electrostatic potential, I show that an active particle accelerator must extend from the vicinity of the neutron star surface to the vicinity of light cylinder. Furthermore, combining the Poisson equation with the Boltzmann equations for electrons/positrons and gamma-rays, and assuming that the gap trans-field thickness is large compared to the longitudinal width, I demonstrate that the energy distribution of ultra-relativistic particles cannot be described by a power-law but by a quasi-monoenergetic distribution at the terminal Lorentz factor. The particles are accelerated in the gap and escape from it with large Lorentz factors. Is is shown that such energetic particles migrating outside of the gap contribute significantly to the gamma-ray luminosity and reproduce the observed softy-ray spectrum between 100 MeV and 3 GeV for the Vela pulsar. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.