Long-term evolution of a merger-remnant neutron star in general relativistic magnetohydrodynamics I: Effect of magnetic winding

Abstract

Long-term ideal and resistive magnetohydrodynamics (MHD) simulations in full general relativity are performed for a massive neutron star formed as a remnant of binary neutron star mergers. Neutrino radiation transport effects are taken into account as in our previous papers. The simulation is performed in axial symmetry and without considering dynamo effects as a first step. In the ideal MHD, the differential rotation of the remnant neutron star amplifies the magnetic-field strength by the winding in the presence of a seed poloidal field until the electromagnetic energy reaches $\sim 10\%$ of the rotational kinetic energy, $E_{\mathrm{kin}}$, of the neutron star. The timescale until the maximum electromagnetic energy is reached depends on the initial magnetic-field strength and it is $\sim 1$ s for the case that the initial maximum magnetic-field strength is $\sim 10^{15}$ G. After a significant amplification of the magnetic-field strength by the winding, the magnetic braking enforces the initially differentially rotating state approximately to a rigidly rotating state. In the presence of the resistivity, the amplification is continued only for the resistive timescale, and if the maximum electromagnetic energy reached is smaller than $\sim 3\%$ of $E_{\mathrm{kin}}$, the initial differential rotation state is approximately preserved. In the present context, the post-merger mass ejection is induced primarily by the neutrino irradiation/heating and the magnetic winding effect plays only a minor role for the mass ejection.

22 pages, 12 figures, accepted for publication in PRD

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• Neutrino emission from binary neutron star mergers: characterizing light curves and mean energies
• Angular Momentum Transport in Proto-Neutron Stars and the Fate of Neutron Star Merger Remnants
• Radiation hydrodynamics modeling of kilonovae with SNEC
• Long-term 3D-MHD Simulations of Black Hole Accretion Disks formed in Neutron Star Mergers
• Impact of a mean field dynamo on neutron star mergers leading to magnetar remnants
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• An extension of Gmunu: General-relativistic resistive magnetohydrodynamics based on staggered-meshed constrained transport with elliptic cleaning
• Quantifying uncertainties in general relativistic magnetohydrodynamic codes
• Geometric and thermodynamic characterization of binary neutron star accretion discs
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• General-relativistic resistive-magnetohydrodynamics simulations of self-consistent magnetized rotating neutron stars
• General relativistic magnetohydrodynamics simulations for binary neutron star mergers