Coherent emission from QED cascades in pulsar polar caps

TL;DR

This study uses 2D particle-in-cell simulations to demonstrate that QED pair cascades in pulsar polar caps can produce coherent radio emission aligned with the magnetic axis, explaining core and conal pulsar signals.

Contribution

First-principles simulations reveal how magnetic field curvature influences pair cascades and leads to coherent radio emission in pulsars.

Findings

Coherent electromagnetic modes are generated near the polar cap edge.

Emission is peaked along the magnetic axis, consistent with pulsar observations.

Magnetic field curvature variation drives bursty pair production and emission.

Abstract

Pulsar magnetospheres are thought to be filled with electron-positron plasma generated in pair cascades. The driving mechanism of these cascades is the emission of gamma-ray photons and their conversion into pairs via Quantum Electrodynamics (QED) processes. In this work, we present 2D particle-in-cell simulations of pair cascades in pulsar polar caps with realistic magnetic field geometry that include the relevant QED processes from first principles. Our results show that, due to variation of magnetic field curvature across the polar cap, pair production bursts self-consistently develop an inclination with respect to the local magnetic field that favors the generation of coherent electromagnetic modes with properties consistent with pulsar radio emission. We show that this emission is peaked along the magnetic axis and close to the polar cap edge and may thus offer an explanation for the core and conal components of pulsar radio emission.