Relativistic Alfvén Waves Entering Charge Starvation in the Magnetospheres of Neutron Stars

Abstract

Instabilities in a neutron star can generate Alfvén waves in its magnetosphere. Propagation along the curved magnetic field lines strongly shears the wave, boosting its electric current $j_{\mathrm{A}}$. We derive an analytic expression for the evolution of the wave vector $\mathbf{k}$ and the growth of $j_{\mathrm{A}}$. In the strongly sheared regime, $j_{\mathrm{A}}$ may exceed the maximum current $j_0$ that can be supported by the background $e^{\pm }$ plasma. We investigate these "charge-starved" waves, first using a simplified two-fluid analytic model, then with first-principles kinetic simulations. We find that the Alfvén wave continues to propagate successfully even when $\kappa \equiv j_{\mathrm{A}}/j_0\gg 1$. It sustains $j_{\mathrm{A}}$ by compressing and advecting the plasma along the magnetic field lines with particle Lorentz factors $\sim {\kappa }^{1/2}$. The simulations show how plasma instabilities lead to gradual dissipation of the wave energy, giving a dissipation power $L_{\mathrm{diss}}\sim 10^{35}(\kappa /100{)}^{1/2}(B_w/10^{11}\mathrm{G})erg/s$, where $B_w$ is the wave amplitude. Our results imply that dissipation due to charge starvation is not sufficient to power observed fast radio bursts (FRBs), in contrast to recent proposals.

arXiv comment9 pages, 5 figures, submitted to ApJ

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Cited by in corpus (10)

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• Periodic Fast Radio Bursts from Luminous X-ray Binaries
• Emission of magnetar bursts and precursors of neutron star mergers
• Transparency of Fast Radio Burst Waves in Magnetar Magnetospheres
• Relativistic Collisionless Shocks in Inhomogeneous Magnetized Plasmas
• Force-free wave interaction in magnetar magnetospheres: Computational modeling in axisymmetry
• Nonlinear Alfvén-wave Dynamics and Premerger Emission from Crustal Oscillations in Neutron Star Mergers
• Fast Radio Bursts as crustal dynamical events induced by magnetic field evolution in young magnetars
• Collisionless tearing instability in relativistic non-thermal pair plasma and its application to MHD turbulence
• Kinetic heating by Alfvén waves in magnetic shears