Gamma-ray Emission from the Vela Pulsar Modeled with the Annular Gap and Core Gap

TL;DR

This paper models the gamma-ray light curves and spectra of the Vela pulsar using a 3D magnetospheric annular and core gap model, explaining observed features and energy dependencies.

Contribution

It introduces a detailed 3D gap model to simulate Vela's gamma-ray emission, linking emission regions to observed light curve features and energy-dependent behaviors.

Findings

Gamma-ray peaks P1 and P2 originate near the null charge surface in the annular gap.

P3 and bridge emissions are generated in the core gap region.

High-energy GeV emission is from curvature radiation, low-energy from secondary synchrotron radiation.

Abstract

The Vela pulsar represents a distinct group of {\gamma}-ray pulsars. Fermi {\gamma}-ray observations reveal that it has two sharp peaks (P1 and P2) in the light curve with a phase separation of 0.42 and a third peak (P3) in the bridge. The location and intensity of P3 are energy-dependent. We use the 3D magnetospheric model for the annular gap and core gap to simulate the {\gamma}-ray light curves, phase-averaged and phase-resolved spectra. We found that the acceleration electric field along a field line in the annular gap region decreases with heights. The emission at high energy GeV band is originated from the curvature radiation of accelerated primary particles, while the synchrotron radiation from secondary particles have some contributions to low energy {\gamma}-ray band (0.1 - 0.3 GeV). The {\gamma}-ray light curve peaks P1 and P2 are generated in the annular gap region near the altitude of null charge surface, whereas P3 and the bridge emission is generated in the core gap region. The intensity and location of P3 at different energy bands depend on the emission altitudes. The radio emission from the Vela pulsar should be generated in a high-altitude narrow regions of the annular gap, which leads to a radio phase lag of ~ 0.13 prior to the first {\gamma}-ray peak.