Jets from neutron-star merger remnants and massive blue kilonovae

Understand

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.