Magneto-elastic oscillations modulating the emission of magnetars

TL;DR

This paper models magneto-elastic oscillations in neutron stars to explain observed QPOs in magnetar flares, linking internal oscillations to external magnetic effects and photon scattering.

Contribution

It introduces a coupled model of neutron star oscillations and magnetospheric scattering, providing new insights into the emission modulation during magnetar flares.

Findings

First results of a self-consistent momentum distribution model

Spectral calculations showing resonant cyclotron scattering effects

Coupling of internal oscillations with external magnetosphere

Abstract

Magneto-elastic oscillations of neutron stars are believed to explain observed quasi-periodic oscillations (QPOs) in the decaying tail of the giant flares of highly magnetized neutron stars (magnetars). Strong efforts of the theoretical modelling from different groups have increased our understanding of this phenomenon significantly. Here, we discuss some constraints on the matter in neutron stars that arise if the interpretation of the observations in terms of superfluid, magneto-elastic oscillations is correct. To explain the observed modulation of the light curve of the giant flare, we describe a model that allows the QPOs to couple to the stellar exterior through the magnetic field. In this magnetosphere, the shaking magnetic field induces currents that provide scattering targets for resonant cyclotron scattering of photons, which is calculated with a Monte-Carlo approach and coupled to a code that calculates the momentum distribution of the charge carriers as a one-dimensional accelerator problem. We show first results of a simplified, but self-consistent momentum distribution, i.e. a waterbag distribution, and of the corresponding spectra.