Milton Ruiz, Antonios Tsokaros, and Stuart L. Shapiro
Date: 22 Oct 2021 arXiv:2110.11968
Abstract
We perform general relativistic magnetohydrodynamic (GRMHD) simulations of quasi-circular, binary neutron stars that merge and undergo delayed or prompt collapse to a black hole (BH). The stars are irrotational and modeled using an SLy or an H4 nuclear equation of state (EOS). To assess the impact of the initial magnetic field configuration on jet launching, we endow the stars with a pure poloidal magnetic field that is initially dynamically unimportant and is either confined to the stellar interior or extends from the interior into the exterior, as in typical pulsars. Consistent with previous results, we find that the BH + disk remnants originating only from binaries that form hypermassive neutron stars (HMNSs) and undergo delayed collapse can drive magnetically-powered jets. We find that the closer the total mass of the binary is to the threshold value for prompt collapse, the shorter is the time delay between the gravitational wave peak amplitude and jet launching. This time delay also strongly depends on the initial magnetic field configuration. We find that seed magnetic field configurations confined to the stellar interior can launch a jet over~$\sim 25\,\rm ms$ later than those with pulsar-like magnetic fields. The lifetime of the jet [$\Delta t\lesssim 150\,\rm ms$] and its outgoing Poynting luminosity [$L_{\rm EM}\sim 10^{52\pm 1}\rm erg/s$] are consistent with the short gamma-ray burst engine lifetime, as well as with the Blandford–Znajek mechanism for launching jets and their associated Poynting luminosities. Our numerical results also suggest that the dynamical ejection of matter can be enhanced by the magnetic field. Therefore, GRMHD studies are required to explain kilonova signals from GW170818-like events.
Jing Zhou, Jinghan Huang, Samuel Qunell, Milton Ruiz, Stuart L. Shapiro, and Antonios Tsokaros