Oscillating pulsar polar gaps

TL;DR

This paper presents an analytical model of oscillating pair creation above pulsar polar caps, describing how large amplitude waves accelerate particles and produce relativistic pair outflows crucial for pulsar wind and polar cap heating prevention.

Contribution

It introduces a formalism for superluminal electrostatic waves in pulsar polar gaps, detailing the transition between low and high-density pair plasma regimes and their oscillatory behaviors.

Findings

Rapid particle acceleration during pair cascade phase.

Oscillating pairs produce large amplitude current oscillations.

Model predicts relativistic pair outflows relevant for pulsar wind.

Abstract

An analytical model for oscillating pair creation above the pulsar polar cap is presented in which the parallel electric field is treated as a large amplitude, superluminal, electrostatic wave. An exact formalism for such wave is derived in one-dimension and applied to both the low-density regime in which the pair plasma density is much lower than the corotating charge density and the high-density regime in which the pair plasma density is much higher than the corotating charge density. In the low-density regime, which is relevant during the phase leading to a pair cascade, a parallel electric field develops resulting in rapid acceleration of particles. The rapid acceleration leads to bursts of pair production and the system switches to the oscillatory phase, corresponding to the high density regime, in which pairs oscillate with net drift motion in the direction of wave propagation. Oscillating pairs lead to a current that oscillates with large amplitude about the Goldreich-Julian current. The drift motion can be highly relativistic if the phase speed of large amplitude waves is moderately higher than the speed of light. Thus, the model predicts a relativistic outflow of pairs, a feature that is required for avoiding overheating of the pulsar polar cap and is also needed for the pulsar wind.