paper

Resolving the fastest ejecta from binary Neutron Star mergers: implications for electromagnetic counterparts

arXiv:2108.08311 · doi:10.3847/1538-4357/ac1f20

Abstract

We examine the effect of spatial resolution on initial mass ejection in grid-based hydrodynamic simulations of binary neutron star mergers. The subset of the dynamical ejecta with velocities greater than c can generate an ultraviolet precursor to the kilonova on hr timescales and contribute to a years-long non-thermal afterglow. Previous work has found differing amounts of this fast ejecta, by one- to two orders of magnitude, when using particle-based or grid-based hydrodynamic methods. Here we carry out a numerical experiment that models the merger as an axisymmetric collision in a co-rotating frame, accounting for Newtonian self-gravity, inertial forces, and gravitational wave losses. The lower computational cost allows us to reach spatial resolutions as high as m, or of the stellar radius. We find that fast ejecta production converges to within for a cell size of m. This suggests that fast ejecta quantities found in existing grid-based merger simulations are unlikely to increase to the level needed to match particle-based results upon further resolution increases. The resulting neutron-powered precursors are in principle detectable out to distances Mpc with upcoming facilities. We also find that head-on collisions at the free-fall speed, relevant for eccentric mergers, yield fast and slow ejecta quantities of order , with a kilonova signature distinct from that of quasi-circular mergers.

arXiv commentAccepted by ApJ

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