The Effect of Different Magnetospheric Structures on Predictions of Gamma-ray Pulsar Light Curves

TL;DR

This study investigates how different magnetospheric magnetic field models influence the predicted gamma-ray pulsar light curves, using geometric modeling and comparison with Fermi LAT data to infer pulsar magnetic structures.

Contribution

It introduces a comparative analysis of static and retarded vacuum dipole magnetic fields in pulsar light curve modeling, constraining the Vela pulsar's magnetic geometry.

Findings

Different B-field models significantly affect light curve shapes.

The retarded vacuum dipole better fits the Vela pulsar data.

Constraints on Vela's magnetic inclination and observer angles.

Abstract

The second pulsar catalogue of the Fermi Large Area Telescope (LAT) will contain in excess of 100 gamma-ray pulsars. The light curves (LCs) of these pulsars exhibit a variety of shapes, and also different relative phase lags with respect to their radio pulses, hinting at distinct underlying emission properties (e.g., inclination and observer angles) for the individual pulsars. Detailed geometric modelling of the radio and gamma-ray LCs may provide constraints on the B-field structure and emission geometry. We used different B-field solutions, including the static vacuum dipole and the retarded vacuum dipole, in conjunction with an existing geometric modelling code, and constructed radiation sky maps and LCs for several different pulsar parameters. Standard emission geometries were assumed, namely the two-pole caustic (TPC) and outer gap (OG) models. The sky maps and LCs of the various B-field and radiation model combinations were compared to study their effect on the resulting LCs. As an application, we compared our model LCs with Fermi LAT data for the Vela pulsar, and inferred the most probable configuration in this case, thereby constraining Vela's high-altitude magnetic structure and system geometry.