HMNS Disk Outflows and the Blue Kilonova from GW170817

The recent detection of the first neutron star (NS) merger in gravitational and electromagnetic waves allows us to compare observational data to theoretical predictions. The observed kilonova from GW170817 was powered by the decay of r-process elements ejected from the system, with the light curve depending on the velocity, mass, and composition of the ejecta. Standard kilonova fits require a separate blue component from lanthanide-poor ejecta. The existence of this component has been used as evidence for a hypermassive NS (HMNS) remnant in GW170817. I will present results from long-term hydrodynamic simulations of the accretion disk around a HMNS that for the first time scan a wide range of plausible parameters compatible with GW170817. We find that large outflow velocities (~0.25c) needed to account for the blue kilonova component, cannot be reproduced by a combination of neutrino heating, viscous angular momentum transport, and nuclear recombination. Viable resolutions to this problem are inclusion of magnetic stresses in long-term disk simulations, improved radiative transfer models for kilonova light curve fitting, or enhancements in the dynamical ejecta from merger simulations.