Luminosity Evolution of Rotation-powered Gamma-ray Pulsars

TL;DR

This paper models the evolution of gamma-ray luminosity in rotation-powered pulsars, linking it to the pulsar's age, envelope composition, and magnetic inclination, providing bounds consistent with observations.

Contribution

It introduces a self-consistent model of the pulsar outer-magnetospheric accelerator, revealing how its structure and gamma-ray luminosity evolve with pulsar age and envelope composition.

Findings

Gamma-ray luminosity remains roughly constant for light element envelopes in early pulsar life.

Luminosity decreases more rapidly for heavy element envelopes as pulsars age.

The model explains the observed distribution bounds of pulsar gamma-ray luminosities.

Abstract

We investigate the electrodynamic structure of a pulsar outer-magnetospheric particle accelerator and the resultant gamma-ray emission. By considering the condition for the accelerator to be self-sustained, we derive how the trans-magnetic-field thickness of the accelerator evolves with the pulsar age. It is found that the thickness is small but increases steadily if the neutron-star envelope is contaminated by sufficient light elements. For such a light element envelope, the gamma-ray luminosity of the accelerator is kept approximately constant as a function of age in the initial ten thousand years, forming the lower bound of the observed distribution of the gamma-ray luminosity of rotation-powered pulsars. If the envelope consists of only heavy elements, on the other hand, the thickness is greater but increases less rapidly than what a light element envelope has. For such a heavy element envelope, the gamma-ray luminosity decreases relatively rapidly, forming the upper bound of the observed distribution. The gamma-ray luminosity of a general pulsar resides between these two extreme cases, reflecting the envelope composition and the magnetic inclination angle with respect to the rotation axis.