Particle acceleration in axisymmetric pulsar current sheets

TL;DR

This study uses 2D particle-in-cell simulations to explore how particle acceleration occurs in pulsar magnetospheres, revealing the role of plasma multiplicity and magnetic dissipation in energizing particles within the current sheet.

Contribution

It provides new insights into particle acceleration mechanisms in axisymmetric pulsar magnetospheres, highlighting the importance of the current sheet and separatrices as sources of high-energy radiation.

Findings

Magnetic dissipation up to 30% within 5 light-cylinder radii in high-multiplicity regimes.

Energetic particles originate from boundary layers between open and closed field lines.

Positrons stream outward, electrons precipitate back, potentially causing auroral-like emissions.

Abstract

The equatorial current sheet in pulsar magnetospheres is often regarded as an ideal site for particle acceleration via relativistic reconnection. Using 2D spherical particle-in-cell simulations, we investigate particle acceleration in the axisymmetric pulsar magnetosphere as a function of the injected plasma multiplicity and magnetization. We observe a clear transition from a highly charge-separated magnetosphere for low plasma injection with little current and spin-down power, to a nearly force-free solution for high plasma multiplicity characterized by a prominent equatorial current sheet and high spin-down power. We find significant magnetic dissipation in the current sheet, up to 30% within 5 light-cylinder radii in the high-multiplicity regime. The simulations unambiguously demonstrate that the dissipated Poynting flux is efficiently channeled to the particles in the sheet, close to the Y-point within about 1-2 light cylinder radii from the star. The mean particle energy in the sheet is given by the upstream plasma magnetization at the light cylinder. The study of particle orbits shows that all energetic particles originate from the boundary layer between the open and the closed field lines. Energetic positrons always stream outward, while high-energy electrons precipitate back towards the star through the sheet and along the separatrices, which may result in auroral-like emission. Our results suggest that the current sheet and the separatrices may be the main source of high-energy radiation in young pulsars.