We analyze a long-lived hyper-massive neutron star merger remnant (post-merger lifetime >250 ms) that has been obtained via large eddy simulations with a gradient subgrid-scale model. We find a clear helicoidal magnetic field structure that is governed by the toroidal component of the magnetic field. Although no jet emerges during the simulation time, we observe at late times a significant increase of the poloidal component of the magnetic field at all scales. We also compare with the results of several binary neutron star simulations with moderate resolution of 120~m, that are evolved up to 50~ms after the merger, which differ in terms of the initial topology and strength of the magnetic field. We find that the best choice is an isotropic small-scale magnetic field distribution that mimics the turbulent state that generically develops during the merger. This initial configuration reaches a closer agreement with our high-resolution simulation results than the purely dipolar large-scale fields that are commonly employed in these type of simulations. This provides a recipe to perform such simulations avoiding the computationally expensive grids required to faithfully capture the amplification of the magnetic field by Kelvin-Helmholtz instabilities.
@article{arxiv.2407.20335,
title = {Delayed jet launching in binary neutron star mergers with realistic initial magnetic fields},
author = {Ricard Aguilera-Miret and Carlos Palenzuela and Federico Carrasco and Stephan Rosswog and Daniele Viganò},
journal= {arXiv preprint arXiv:2407.20335},
year = {2024}
}