Dead zone in the polar-cap accelerator of pulsars

TL;DR

This study uses time-dependent simulations to analyze plasma flows in pulsar polar caps, revealing a 'dead zone' where particle acceleration is inefficient, influencing pulsar emission structures and the development of outer gaps.

Contribution

The paper introduces a self-consistent simulation approach to identify the dead zone in pulsar polar caps and its implications for pulsar emission and gap formation.

Findings

Identification of a dead zone where particle acceleration is suppressed

Prediction of hollow-cone radio emission structure in pulsars

Observation of two-stream instability in mixed ion flows

Abstract

We study plasma flows above pulsar polar caps using time-dependent simulations of plasma particles in the self-consistent electric field. The flow behavior is controlled by the dimensionless parameter alpha=(j/c rho_GJ) where j is the electric current density and rho_GJ is the Goldreich-Julian charge density. The region of the polar cap where 0<alpha<1 is a "dead zone" --- in this zone particle acceleration is inefficient and pair creation is not expected even for young, rapidly rotating pulsars. Pulsars with polar caps near the rotation axis are predicted to have a hollow-cone structure of radio emission, as the dead zone occupies the central part of the polar cap. Our results apply to charge-separated flows of electrons (j<0) or ions (j>0). In the latter case, we consider the possibility of a mixed flow consisting of different ion species, and observe the development of two-stream instability. The dead zone at the polar cap is essential for the development of an outer gap near the null surface rho_GJ=0.