Pulsar Outer-gap Electrodynamics: Hardening of Spectral Shape in the Trailing Peak in Gamma-ray Light Curve

TL;DR

This paper investigates how the spectral shape of gamma-ray emission from pulsar outer gaps hardens in the trailing peak, showing that the cutoff energy varies with rotation phase due to particle acceleration differences.

Contribution

It demonstrates that the cutoff energy of curvature radiation evolves with pulsar rotation phase, explaining the spectral hardening in the trailing peak.

Findings

Cutoff energy varies with rotation phase.

Higher Lorentz factors in trailing side lead to more energetic gamma-rays.

Spectral hardening occurs in the trailing peak of gamma-ray light curves.

Abstract

The spectral characteristics of the pulsed gamma-ray emission from outer-magnetospheric particle accelerators are investigated. Either positrons or electrons are accelerated outwards by the magnetic-field-aligned electric field to emit gamma-rays via curvature process. Since the particles move along relatively straight paths in the trailing side of a rotating magnetosphere, they attain higher Lorentz factors to emit more energetic gamma-rays than those in the leading side. It is first demonstrated that the cutoff energy of the curvature radiation evolves with the rotation phase owing to the variation of the curvature radii of the particle paths and maximizes at a slightly later phase of the trailing peak in the gamma-ray light curve.