Particle Accelerator in Pulsar Magnetospheres: Super‐Goldreich‐Julian Current with Ion Emission from the Neutron Star Surface

We investigate the self-consistent electrodynamic structure of a particleaccelerator in the Crab pulsar magnetosphere on the two-dimensional poloidalplane, solving the Poisson equation for the electrostatic potential togetherwith the Boltzmann equations for electrons, positrons and gamma-rays. If thetrans-field thickness of the gap is thin, the created current density becomessub-Goldreich-Julian, giving the traditional outer-gap solution but withnegligible gamma-ray luminosity. As the thickness increases, the createdcurrent increases to become super-Goldreich-Julian, giving a new gap solutionwith substantially screened acceleration electric field in the inner part. Inthis case, the gap extends towards the neutron star with a small-amplitudepositive acceleration field, extracting ions from the stellar surface as aspace-charge-limited flow. The acceleration field is highly unscreened in theouter magnetosphere, resulting in a gamma-ray spectral shape which isconsistent with the observations.Comment: 36 pages, 14 figures, accepted to Astroph.