Numerical Simulations of Equatorially-Asymmetric Magnetized Supernovae: Formation of Magnetars and Their Kicks

TL;DR

This study uses numerical simulations to explore how offset magnetic fields in magnetorotational supernovae influence asymmetric explosions and magnetar kicks, predicting velocities up to 1000 km/s, which can inform future observations.

Contribution

It demonstrates that offset magnetic fields cause equatorially-asymmetric supernova explosions and significant magnetar kicks, a novel insight into supernova dynamics and magnetar formation.

Findings

Magnetar kicks can reach 1000 km/s.

Magnetic pressure drives the acceleration of the magnetar.

Asymmetric explosions produce bipolar jets.

Abstract

A series of numerical simulations on magnetorotational core-collapse supernovae are carried out. Dipole-like configurations which are offset northward are assumed for the initially strong magnetic fields together with rapid differential rotations. Aims of our study are to investigate effects of the offset magnetic field on magnetar kicks and on supernova dynamics. Note that we study a regime where the proto-neutron star formed after collapse has a large magnetic field strength approaching that of a ``magnetar'', a highly magnetized slowly rotating neutron star. As a result, equatorially-asymmetric explosions occur with a formation of the bipolar jets. Resultant magnetar's kick velocities are $\sim 300-1000$ km s$^{-1}$. We find that the acceleration is mainly due to the magnetic pressure while the somewhat weaker magnetic tension works toward the opposite direction, which is due to stronger magnetic field in the northern hemisphere. Noted that observations of magnetar's proper motions are very scarce, our results supply a prediction for future observations. Namely, magnetars possibly have large kick velocities, several hundred km s$^{-1}$, as ordinary neutron stars do, and in an extreme case they could have those up to 1000 km s$^{-1}$.