Jets from neutron-star merger remnants and massive blue kilonovae

Abstract

We perform high-resolution three-dimensional general-relativistic magnetohydrodynamic simulations with neutrino transport of binary neutron star (BNS) mergers resulting in a long-lived remnant neutron star, with properties typical of galactic BNS and consistent with those inferred for the first observed BNS merger GW170817. We demonstrate self-consistently that within $\lesssim 30$ ms post-merger magnetized ($\sigma \sim 5-10$) twin polar jets emerge with asymptotic Lorentz factor $\Gamma \sim 5-10$, which successfully break out from the merger debris within $\lesssim 20$ ms. A fast ($v\lesssim 0.6c$), magnetized ($\sigma \sim 0.1$) wind surrounds the jet core and generates a UV/blue kilonova precursor on timescales of hours, similar to the precursor signal due to free neutron decay in fast dynamical ejecta. Post-merger ejecta are quickly dominated by MHD-driven outflows from an accretion disk. We demonstrate that within only 50 ms post-merger, $\gtrsim 2\times 10^{-2}{M}_{\odot }$ of lanthanide-free, quasi-spherical ejecta with velocity $\sim 0.1c$ is launched, yielding a kilonova signal consistent with GW170817 on timescales of $\lesssim 5$\,d.

Accepted for publication in Physical Review Letters. 5 + 5 pages, 18 figures