Three-dimensional Two-Layer Outer Gap Model: the Third Peak of Vela Pulsar

TL;DR

This paper develops a three-dimensional two-layer outer gap model for the Vela pulsar to explain the observed third peak in its gamma-ray light curve and its energy-dependent phase shift, revealing the importance of azimuthal gap structure.

Contribution

It introduces a 3D two-layer outer gap model to explain complex gamma-ray features of the Vela pulsar, including the third peak and its energy dependence.

Findings

The model reproduces the third peak in Vela's gamma-ray light curve.

The third peak's phase position shifts with photon energy.

Azimuthal structure of the outer gap explains the third peak's behavior.

Abstract

We extend the two-dimensional two-layer outer gap model to a three-dimensional geometry and use it to study the high-energy emission of the Vela pulsar. We apply this three-dimensional two-layer model to the Vela pulsar and compare the model light curves, the phase-averaged spectrum and the phase-resolved spectra with the recent Fermi observations, which also reveals the existence of the third peak between two main peaks. The phase position of the third peak moves with the photon energy, which cannot be explained by the geometry of magnetic field structure and the caustic effect of the photon propagation. We suggest that the existence of the third peak and its energy dependent movement results from the azimuthal structure of the outer gap.