NEUTRINO SIGNATURES AND THE NEUTRINO-DRIVEN WIND IN BINARY NEUTRON STAR MERGERS

We present VULCAN/2D multigroup flux-limited-diffusion radiation-hydrodynamics simulations of binary neutron star mergers, using the Shen equation of state, covering greater than or similar to 100 ms, and starting from azimuthal-averaged two-dimensional slices obtained from three-dimensional smooth-particle-hydrodynamics simulations of Rosswog & Price for 1.4 M-circle dot(baryonic) neutron stars with no initial spins, co-rotating spins, or counter-rotating spins. Snapshots are post-processed at 10 ms intervals with a multiangle neutrino-transport solver. We find polar-enhanced neutrino luminosities, dominated by (nu) over bar (e) and nu(mu) neutrinos at the peak, although nu(e) emission may be stronger at late times. We obtain typical peak neutrino energies for nu(e), (nu) over bar (e), and nu(mu) of similar to 12, similar to 16, and similar to 22 MeV, respectively. The supermassive neutron star (SMNS) formed from the merger has a cooling timescale of less than or similar to 1 s. Charge-current neutrino reactions lead to the formation of a thermally driven bipolar wind with < M > similar to 10(-3) M-circle dot s(-1) and baryon-loading in the polar regions, preventing any production of a gamma-ray burst prior to black hole formation. The large budget of rotational free energy suggests that magneto-rotational effects could produce a much-greater polar mass loss. We estimate that less than or similar to 10(-4) M-circle dot of material with an electron fraction in the range 0.1-0.2 becomes unbound during this SMNS phase as a result of neutrino heating. We present a new formalism to compute the nu(i)(nu) over bar (i) annihilation rate based on moments of the neutrino-specific intensity computed with our multiangle solver. Cumulative annihilation rates, which decay as similar to t(-1.8), decrease over our 100 ms window from a few x10(50) to similar to 10(49) erg s(-1), equivalent to a few x10(54) to similar to 10(53) e(-)e(+) pairs per second.