You Must Construct Additional Hypermassive Neutron Stars

Abstract

We examine the long-term evolution of accretion tori around the remnants of compact object mergers and the explosions of highly magnetized massive stars to better understand their roles in the creation of optical transients and the synthesis of r-process elements. We begin by modifying the FLASH4.5 code to evolve magnetohydrodynamics with simple neutrino transport and a realistic equation of state in 3D spherical coordinates, and provide verification tests. With this new framework, we evolve post-merger systems of tori around black holes and hypermassive neutron stars. We find that magnetic stresses, neutrino driven winds, and thermal effects eject outflows with a broad range of electron fractions, velocities and entropies, sufficient to power kilonovae and produce up to 3rd peak r-process elements. While the ejecta from our simulations cannot match the masses and velocities inferred from two component kilonova modelling of GW170817, more detailed multidimensional kilonova models are needed to see if our outflows are consistent with observations of the blue kilonova. Finally, we detail the modifications to the neutrino scheme and treatment of gravity in FLASH4.5 necessary to run simulations of magnetorotational supernovae, along with further verification tests.