High‐Energy Emission from Pulsar Outer Magnetospheres

We investigate a stationary pair production cascade in the outermagnetosphere of an isolated, spinning neutron star. The charge depletion dueto global flows of charged particles, causes a large electric field along themagnetic field lines. Migratory electrons and/or positrons are accelerated bythis field to radiate gamma-rays via curvature and inverse-Compton processes.Some of such gamma-rays collide with the X-rays to materialize as pairs in thegap. The replenished charges partially screen the electric field, which isself-consistently solved together with the energy distribution of particles andgamma-rays at each point along the field lines. By solving the set of Maxwelland Boltzmann equations, we demonstrate that an external injection of chargedparticles at nearly Goldreich-Julian rate does not quench the gap but shiftsits position and that the particle energy distribution cannot be described by apower-law. The injected particles are accelerated in the gap and escape from itwith large Lorentz factors. We show that such escaping particles migratingoutside of the gap contribute significantly to the gamma-ray luminosity foryoung pulsars and that the soft gamma-ray spectrum between 100 MeV and 3 GeVobserved for the Vela pulsar can be explained by this component. We alsodiscuss that the luminosity of the gamma-rays emitted by the escaping particlesis naturally proportional to the square root of the spin-down luminosity.Comment: 24 pages, 11 figures; to appear in the inaugural (Sep) issue of Progress in Astrophysics Researches (a new book series