Modeling high-energy pulsar lightcurves from first principles

TL;DR

This paper uses 3D particle-in-cell simulations to self-consistently model pulsar magnetospheres, revealing the origins of gamma-ray emissions and their dependence on viewing angles, which improves understanding of pulsar lightcurves.

Contribution

It introduces a self-consistent 3D simulation approach to model pulsar magnetospheres and gamma-ray emission mechanisms from first principles.

Findings

High-energy emission originates from the Y-point and current sheet regions.

Synthetic lightcurves typically show two peaks with caustics, and secondary peaks can occur at high obliquity.

Radiative efficiency varies with viewing angle and pulsar inclination.

Abstract

Current models of gamma-ray lightcurves in pulsars suffer from large uncertainties on the precise location of particle acceleration and radiation. Here, we present an attempt to alleviate these difficulties by solving for the electromagnetic structure of the oblique magnetosphere, particle acceleration, and the emission of radiation self-consistently, using 3D spherical particle-in-cell simulations. We find that the low-energy radiation is synchro-curvature radiation from the polar-cap regions within the light cylinder. In contrast, the high-energy emission is synchrotron radiation that originates exclusively from the Y-point and the equatorial current sheet where relativistic magnetic reconnection accelerates particles. In most cases, synthetic high-energy lightcurves contain two peaks that form when the current sheet sweeps across the observer's line of sight. We find clear evidence of caustics in the emission pattern from the current sheet. High-obliquity solutions can present up to two additional secondary peaks from energetic particles in the wind region accelerated by the reconnection-induced flow near the current sheet. The high-energy radiative efficiency depends sensitively on the viewing angle, and decreases with increasing pulsar inclination. The high-energy emission is concentrated in the equatorial regions where most of the pulsar spindown is released and dissipated. These results have important implications for the interpretation of gamma-ray pulsar data.