Impact of Neutrino Interactions on Outflows of Neutron-Star Mergers

Abstract

Despite significant progress in the recent years a robust identification of the main astrophysical source or sources of the rapid-neutron-capture (r-) process is still lacking. Neutrino-driven winds in ordinary core-collapse supernovae seem to be ruled out as main r-process sources because of their insufficiently low neutron densities and entropies. Magnetorotationally driven supernovae might provide r-process conditions, but only if the magnetic field is strong enough (or builds up quickly enough) to launch the explosion on a sufficiently short timescale; if or for how many progenitors this condition is met is largely unclear at the moment. Neutron-star (NS) mergers, i.e. mergers of two NSs or of a NS with a black hole (BH), could robustly produce r-process viable outflows in most events and by means of multiple ejecta components. Using a combination of neutrino-hydrodynamics simulations and post-processing nucleosynthesis calculations we investigated the different ejecta components and their r-process yields. Apart from the massive, nucleosynthesis relevant outflows also ultrarelativistic jets could emerge from the remnant of a NS merger. These jets are widely believed to explain the still mysterious origin of short gamma-ray bursts (sGRBs), but the main agent launching the jet remains disputed. We outline a recent study that explores one popular scenario in which the jet is being driven entirely due to heating by pair-annihilation of neutrinos.

Three-dimensional Boltzmann-Hydro Code for Core-collapse in Massive Stars. II. The Implementation of Moving-mesh for Neutron Star Kicks

“…The neutrino radiation-hydrodynamic simulations of CCSNe have made a remarkable progress with ever increasing computational resources in the last few decades (for the current status, see e.g., Ott et al 2008;Müller et al 2012;Bruenn et al 2014;Takiwaki et al 2014;Dolence et al 2015;Just et al 2015;Kuroda et al 2015;Lentz et al 2015). Although the present interest of supernova society is directed mainly to 3D hydrodynamical aspects, neutrino transfer is certainly one of the most important ingredients in realistic modeling of CCSNe.…”

“…As a matter of fact, various approximations have been employed even in the most sophisticated multi-dimensional simulations, which include the multi-group flux-limited diffusion (MGFLD) (Mezzacappa et al 1998;Walder et al 2005;Zhang et al 2013;Dolence et al 2015), isotropic diffusion source approximation (IDSA) (Liebendörfer et al 2009;Suwa et al 2010;Takiwaki et al 2014;Pan et al 2016), two-moment method (Just et al 2015;O'Connor & Couch 2015;Skinner et al 2015), fast-multi-group transport (FMT) method (Müller & Janka 2015), variable Eddington tensor method (Müller et al 2012) and 2D Boltzmann transport method without v/c corrections (Livne et al 2004;Ott et al 2008); some of them (Müller et al 2012;Bruenn et al 2014;Lentz et al 2015) employ the ray-by-ray plus approximation further. It should be stressed that some of these approximations have been validated only under spherical symmetry and their performance in nonspherical situations, which no doubt prevail in the post-bounce supernova core, are still uncertain (see some also Buras et al 2006b;Skinner et al 2015 for the validation of the ray-by-ray approximation).…”