The Net Advance of Physics: Gamma-Ray Pulsar Emission Models, by Alice K. Harding -- Section 1.

Introduction

As the number of -ray pulsars has grown from two to eight over

the five years since the launch of CGRO, the amount of new data

on these objects has provided many puzzles, some clues, but few

definitive answers. Rather, the models for -ray pulsars that were

proposed and investigated in the pre-CGRO era have been

evolving in light of the new results. There are currently two types of

-ray pulsar models being studied in detail. Polar cap models

assume that particles are accelerated along open field lines near the

neutron star by parallel electric fields and induce pair cascades by

either curvature radiation (Daugherty & Harding 1982, Usov &

Melrose 1995) or inverse-Compton radiation (Dermer & Sturner

1994). Outer gap models assume that primary particles are

accelerated in vacuum gaps in the outer magnetosphere and induce

pair cascades through - pair production (Cheng, Ho &

Ruderman 1986; Romani & Yadigaroglu 1995). In addition, there

are ideas for generating pulsed -ray emission at the light cylinder

(Lyubarski 1996) or in vacuum fields in the magnetosphere (Higgins

& Henriksen 1996). With the larger number of observed -ray

pulsars and the improved sensitivity of the detectors, predictions of

the models can now be tested and their parameters more tightly

constrained.

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