One-dimensional electric field structure of an outer gap accelerator — I. γ-ray production resulting from curvature radiation

Abstract

We study the structure of a stationary and axisymmetric charge-deficient region (or potential gap) in the outer magnetosphere of a spinning neutron star. Assuming the existence of global current flow patterns in the magnetosphere, the charge depletion causes a large electric field along the magnetic field lines. This longitudinal electric field accelerates migratory electrons and/or positrons to ultrarelativistic energies. These relativistic electrons/positrons radiate g-ray photons by curvature radiation. These g-rays, in turn, produce yet more radiating particles by colliding with ambient X-ray photons, leading to a pair production cascade in the gap. The replenished charges partially screen the longitudinal electric field, which is selfconsistently solved together with the distribution of e ^ and g-ray photons. We find the voltage drop in the gap as a function of the soft photon luminosity. It is demonstrated that the voltage drop is less than 3 � 10 13 V when the background X-ray radiation is as luminous as Vela. However, this value increases with decreasing X-ray luminosity and attains 3 � 10 15 V when the X-ray luminosity is as low as LX ˆ 10 31 ergs 21 .