Neutrino signatures and the neutrino-driven wind in Binary Neutron Star Mergers

Luc Dessart; Christian Ott; Adam Burrows; Stefan Rosswog; Eli Livne

doi:10.1088/0004-637X/690/2/1681

paper

Neutrino signatures and the neutrino-driven wind in Binary Neutron Star Mergers

arXiv:0806.4380 · doi:10.1088/0004-637X/690/2/1681

Abstract

We present VULCAN/2D multi-group flux-limited-diffusion radiation hydrodynamics simulations of binary neutron star (BNS) mergers, using the Shen equation of state, covering ~100 ms, and starting from azimuthal-averaged 2D slices obtained from 3D SPH simulations of Rosswog & Price for 1.4 Msun (baryonic) neutron stars with no initial spins, co-rotating spins, and counter-rotating spins. Snapshots are post-processed at 10 ms intervals with a multi-angle neutrino-transport solver. We find polar-enhanced neutrino luminosities, dominated by $ν ˉ_{e}$ and `` $ν_{μ}$ '' neutrinos at peak, although $ν_{e}$ emission may be stronger at late times. We obtain typical peak neutrino energies for $ν_{e}$ , $ν ˉ_{e}$ , and `` $ν_{μ}$ '' of ~12, ~16, and ~22 MeV. The super-massive neutron star (SMNS) formed from the merger has a cooling timescale of ~1 s. Charge-current neutrino reactions lead to the formation of a thermally-driven bipolar wind with < $M ˙$ > ~10 $^{- 3}$ Msun/s, baryon-loading the polar regions, and preventing any production of a GRB prior to black-hole formation. The large budget of rotational free energy suggests magneto-rotational effects could produce a much greater polar mass loss. We estimate that ~10 $^{- 4}$ Msun of material with electron fraction in the range 0.1-0.2 become unbound during this SMNS phase as a result of neutrino heating. We present a new formalism to compute the $ν_{i} ν ˉ_{i}$ annihilation rate based on moments of the neutrino specific intensity computed with our multi-angle solver. Cumulative annihilation rates, which decay as $t^{- 1.8}$ , decrease over our 100 ms window from a few 10 $^{50}$ to ~10 $^{49}$ erg/s, equivalent to a few 10 $^{54}$ to ~10 $^{53}$ $e^{-} e^{+}$ pairs per second.

23 pages, 20 figures, 2 tables, submitted to ApJ, high resolution version of the paper available at http://hermes.as.arizona.edu/~luc/ms.pdf

Neutrino signatures and the neutrino-driven wind in Binary Neutron Star Mergers

Abstract

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