High-Altitude Particle Acceleration and Radiation in Pulsar Slot Gaps

We explore the pulsar slot gap (SG) electrodynamics up to very high altitudes, where for most relatively rapidly rotating pulsars both the standard small-angle approximation and the assumption that the magnetic field lines are ideal streamlines break down. We address the importance of the electrodynamic conditions at the SG boundaries and the occurrence of a steady state drift of charged particles across the SG field lines at very high altitudes. These boundary conditions and the deviation of particle trajectories from streamlines determine the asymptotic behavior of the scalar potential at all radii from the polar cap (PC) to near the light cylinder. As a result, we demonstrate that the steady state accelerating electric field, E_∥, must approach a small and constant value at high altitude above the PC. This E_∥ is capable of maintaining electrons moving with high Lorentz factors (~few × 10⁷) and emitting curvature γ-ray photons up to nearly the light cylinder. By numerical simulations, we show that primary electrons accelerating from the PC surface to high altitude in the SG along the outer edge of the open field region will form caustic emission patterns on the trailing dipole field lines. Acceleration and emission in such an extended SG may form the physical basis of a model that can successfully reproduce some pulsar high-energy light curves.