Magnetar field evolution and crustal plasticity

TL;DR

This paper proposes a new model for magnetar magnetic field evolution driven by crustal plastic flow, challenging previous assumptions of static crustal lattice evolution, and explores implications for magnetar activity and flare energy release.

Contribution

It introduces a novel mechanism of magnetic flux transport via crustal plasticity, expanding understanding of magnetar magnetic field evolution beyond Hall drift and Ohmic decay.

Findings

Plastic flow can induce significant magnetic flux transport in magnetar crusts.

Estimated magnetic field strengths necessary for plastic flow vary with crustal depth.

Core-superconductivity interactions may influence magnetic evolution depending on star's spindown history.

Abstract

The activity of magnetars is believed to be powered by colossal magnetic energy reservoirs. We sketch an evolutionary picture in which internal field evolution in magnetars generates a twisted corona, form which energy may be released suddenly in a single giant flare, or more gradually through smaller outbursts and persistent emission. Given the ages of magnetars and the energy of their giant flares, we suggest that their evolution is driven by a novel mechanism: magnetic flux transport/decay due to persistent plastic flow in the crust, which would invalidate the common assumption that the crustal lattice is static and evolves only under Hall drift and Ohmic decay. We estimate the field strength required to induce plastic flow as a function of crustal depth, and the viscosity of the plastic phase. The star's superconducting core may also play a role in magnetar field evolution, depending on the star's spindown history and how rotational vortices and magnetic fluxtubes interact.