The imprint of pulsar parameters on the morphology of Pulsar Wind Nebulae

TL;DR

This study uses relativistic MHD simulations to explore how pulsar parameters like obliquity and wind magnetization influence the diverse morphologies of Pulsar Wind Nebulae, matching observations of Vela and Crab.

Contribution

It introduces a new parametrization of pulsar wind based on Force Free Electrodynamics simulations to analyze nebula morphology dependence on pulsar properties.

Findings

Vela's morphology is reproduced with high wind magnetization and obliquity ~45°.

Crab-like morphology occurs with low magnetization and obliquity ≥ 45°.

Kelvin-Helmholtz instabilities cause small-scale turbulence downstream of the reverse shock.

Abstract

The morphology of young Pulsar Wind Nebulae (PWN) is largely determined by the properties of the wind injected by the pulsar. We have used a recent parametrization of the wind obtained from Force Free Electrodynamics simulations of pulsar magnetospheres to simulate nebulae for different sets of pulsar parameters. We performed axisymmetric Relativistic Magnetohydrodynamics simulations to test the morphology dependence of the nebula on the obliquity of the pulsar and on the magnetization of the pulsar wind. We compare these simulations to the morphology of the Vela and Crab PWN. We find that the morphology of Vela can be reproduced qualitatively if the pulsar obliquity angle is alpha ~45deg and the magnetization of the wind is high (sigma_0 ~ 3.0). A morphology similar to the one of the Crab Nebula is only obtained for low magnetization simulations with alpha >~ 45deg. Interestingly, we find that Kelvin-Helmholtz instabilities produce small scale turbulences downstream of the reverse shock of the pulsar wind.