Classical, large scale 3D MHD simulations of interacting pulsar wind nebulae

TL;DR

This study uses large-scale 3D MHD simulations to investigate how the angle between a pulsar's rotation axis and the interstellar magnetic field influences the shape and radio emission of pulsar wind nebulae around static massive stars.

Contribution

It introduces detailed 3D MHD models to analyze the impact of magnetic field orientation on pulsar wind nebula morphology and radio properties, advancing understanding of their observable structures.

Findings

Pulsar wind nebula shapes vary with magnetic field angle, appearing as rectangles, circles, or irregular shapes.

The orientation affects the non-thermal radio emission distribution.

Material mixing in older nebulae is less influenced by the magnetic field angle.

Abstract

Magnetized rotating neutron stars, or pulsars, are a possible end product of massive star evolution. Their relativistic wind successively interacts with the supernova ejecta of their defunct progenitor, then with the circumstellar medium of the progenitor, and eventually with the interstellar medium. If a massive star is static with respect to its ambient medium, then its resulting circumstellar medium is elongated along the direction of the local magnetic field, and its supernova remnant transiently appears as a rectangle. The pulsar wind nebula forming in it is, in its turn, elongated, as long as the pulsar axis of rotation matches the direction of the local magnetization. In this work, we explore how the angle between the direction of the local magnetic field of the interstellar medium and the pulsar axis of rotation influences the shaping of its pulsar wind nebula with 3D MHD simulations are carried out with the PLUTO. We use those models to perform radiative transfer calculations to derive non-thermal radio emission maps of the pulsar wind nebulae. When the polar elongation of the pulsar develop, they bend in opposite directions under the effects of the cavity carved by the stellar wind and already filled by supernova ejecta. This induces a complex distribution of magnetized supernova ejecta and pulsar wind, resulting in various observable structures, appearing as rectangles, circles, or irregular oblong shapes, in the radio waveband. The angle between the direction of the pulsar rotation axis and that of the local ambient magnetization is a governing parameter for the shaping and non-thermal radio properties of the pulsar wind nebulae of static massive stars; however, the mixing of material, once the pulsar wind nebula is old (50 to 80 kyr), is not strongly affected by that factor.