Neutrino Signatures and the Neutrino-Driven Wind in Binary Neutron Star Mergers
Abstract
We present VULCAN/2D multigroup flux-limited-diffusion radiation-hydrodynamics simulations of binary neutron star mergers, using the Shen equation of state, covering gsim 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 sun(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 {\bar ν}_e and "νμ" neutrinos at the peak, although ν e emission may be stronger at late times. We obtain typical peak neutrino energies for ν e , {\bar ν}_e, and "νμ" of ~ 12, ~ 16, and ~ 22 MeV, respectively. The supermassive neutron star (SMNS) formed from the merger has a cooling timescale of lsim 1 s. Charge-current neutrino reactions lead to the formation of a thermally driven bipolar wind with <\dot{M}> ∼ 10-3 M sun s-1 and baryon-loading in the polar regions, preventing any production of a γ-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 lsim 10-4 M sun 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 ν_i{\bar ν}_i annihilation rate based on moments of the neutrino-specific intensity computed with our multiangle solver. Cumulative annihilation rates, which decay as ~t -1.8, decrease over our 100 ms window from a few ×1050 to ~ 1049 erg s-1, equivalent to a few ×1054 to ~ 1053 e-e+ pairs per second.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2009
- DOI:
- 10.1088/0004-637X/690/2/1681
- arXiv:
- arXiv:0806.4380
- Bibcode:
- 2009ApJ...690.1681D
- Keywords:
-
- gamma rays: bursts;
- hydrodynamics;
- neutrinos;
- stars: neutron;
- stars: rotation;
- supernovae: general;
- Astrophysics
- E-Print:
- 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