Pulsar Emission Geometry and Accelerating Field Strength

TL;DR

This paper models gamma-ray pulsar light curves using geometrical emission models and field configurations, estimating the accelerating electric field and constraining emission geometry with Fermi LAT data.

Contribution

It introduces a Markov Chain Monte Carlo approach to fit pulsar emission models and estimates the electric field dependence on radius based on spectral data.

Findings

Vacuum field models better match observed light curves.

Estimated electric field constrains emission geometry.

Modeling results support curvature radiation dominance.

Abstract

The high-quality Fermi LAT observations of gamma-ray pulsars have opened a new window to understanding the generation mechanisms of high-energy emission from these systems. The high statistics allow for careful modeling of the light curve features as well as for phase resolved spectral modeling. We modeled the LAT light curves of the Vela and CTA 1 pulsars with simulated high-energy light curves generated from geometrical representations of the outer gap and slot gap emission models, within the vacuum retarded dipole and force-free fields. A Markov Chain Monte Carlo maximum likelihood method was used to explore the phase space of the magnetic inclination angle, viewing angle, maximum emission radius, and gap width. We also used the measured spectral cutoff energies to estimate the accelerating parallel electric field dependence on radius, under the assumptions that the high-energy emission is dominated by curvature radiation and the geometry (radius of emission and minimum radius of curvature of the magnetic field lines) is determined by the best fitting light curves for each model. We find that light curves from the vacuum field more closely match the observed light curves and multiwavelength constraints, and that the calculated parallel electric field can place additional constraints on the emission geometry.