On the Origin of Pulsar and Magnetar Magnetic Fields

TL;DR

This paper investigates the origin of neutron star magnetic fields, proposing that dynamo processes during core collapse can naturally produce the strong fields observed in magnetars and pulsars, influenced by stellar rotation rates.

Contribution

It links dynamo theory and 3D simulations to neutron star magnetic field generation, explaining the magnetar-pulsar dichotomy through core rotation variations.

Findings

Proto-neutron stars can generate ~10^15 G magnetic fields via convective dynamos.

The magnetar/pulsar magnetic field difference may result from core rotation rate distribution.

Simulations show vigorous convection leads to strong dipole fields in progenitors.

Abstract

In order to address the generation of neutron star magnetic fields, with particular focus on the dichotomy between magnetars and radio pulsars, we consider the properties of dynamos as inferred from other astrophysical systems. With sufficiently low (modified) Rossby number, convective dynamos are known to produce dipole-dominated fields whose strength scales with convective flux, and we argue that these expectations should apply to the convective proto-neutron stars at the centers of core-collapse supernovae. We analyze a suite of three-dimensional simulations of core collapse, featuring a realistic equation of state and full neutrino transport, in this context. All our progenitor models, ranging from 9 solar masses to 25 solar masses, including one with initial rotation, have sufficiently vigorous proto-neutron-star convection to generate dipole fields of order ~10^15 gauss, if the modified Rossby number resides in the critical range. Thus, the magnetar/radio pulsar dichotomy may arise naturally in part from the distribution of core rotation rates in massive stars.