Plastic damping of Alfv\'en waves in magnetar flares and delayed afterglow emission

TL;DR

This paper investigates how Alfvén waves generated by magnetar flares penetrate the star, causing crustal heating and delayed afterglow emission, with implications for understanding neutron star magnetospheres.

Contribution

It introduces a model of wave transmission and plastic crustal response explaining delayed afterglow in magnetars, a novel mechanism linking flare energy to surface emission.

Findings

Alfvén waves can transmit energy into the neutron star crust within 10 ms.

Crustal plastic flow heats the crust, leading to long-term afterglow emission.

Significant energy is lost via neutrino emission and core conduction.

Abstract

Magnetar flares generate Alfv\'en waves bouncing in the closed magnetosphere with energy up to $\sim 10^{46}$ erg. We show that on a 10-ms timescale the waves are transmitted into the star and form a compressed packet of high energy density. This packet strongly shears the stellar crust and initiates a plastic flow, heating the crust and melting it hundreds of meters below the surface. A fraction of the deposited plastic heat is eventually conducted to the stellar surface, contributing to the surface afterglow months to years after the flare. A large fraction of heat is lost to neutrino emission or conducted into the core of the neutron star.