A three-dimensional outer-magnetospheric gap model for gamma-ray pulsars: I. The crab pulsar

Abstract

We use a three-dimensional pulsar magnetosphere model to study the geometry of outer-magnetospheric gaps. The vertical size of the 'outer gap' is first determined by a self-consistent model in which the outer gap size is limited by pair production from collisions between (1) thermal photons produced from polar cap heating by backflow 'outer gap' current, and (2) the curvature photons emitted by gap-accelerated charged particles. The transverse size of the outer gap is also determined by local pair production limits. In principle, there are two topologically disconnected outer gaps in the magnetosphere of a pulsar. Both incoming and outgoing particle flows are allowed. However, the emission morphologies produced by incoming particle flow is severely restricted by local pair production in the gap and the absorption of magnetic pair production near the star. Double-peaked light curves with strong bridges are most common. From the three-dimensional structure of the outer gap and its local properties, we calculate the emission morphologies and phase-resolved spectra of gamma-ray pulsars. Applications to the Crab pulsar illustrate the model.