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| Title: |
| Neutrino Pair Annihilation in Collapsars: A Ray-tracing Method in Special Relativity |
| Authors: |
| Harikae, Seiji; Kotake, Kei; Takiwaki, Tomoya |
| Affiliation: |
| AA(Department of Astronomy, The Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,Tokyo 113-0033, Japan ; Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan ; seiji.harikae@nao.ac.jp), AB(Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan ; Center for Computational Astrophysics, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan), AC(Division of Theoretical Astronomy, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan ) |
| Publication: |
| The Astrophysical Journal, Volume 713, Issue 1, pp. 304-317 (2010). (ApJ Homepage) |
| Publication Date: |
| 04/2010 |
| Origin: |
| IOP |
| ApJ Keywords: |
| accretion, accretion disks, gamma-ray burst: general, magnetohydrodynamics: MHD, methods: numerical, neutrinos, supernovae: general |
| DOI: |
| 10.1088/0004-637X/713/1/304 |
| Bibliographic Code: |
| 2010ApJ...713..304H |
Abstract
We develop a numerical scheme and code for estimating the energy and momentum transfer via neutrino pair annihilation (\nu + {\bar{\nu }} \rightarrow e^{-}+ e^{+}), bearing in mind the application to the collapsar models of gamma-ray bursts (GRBs). To calculate the neutrino flux illuminated from the accretion disk, we perform a ray-tracing calculation in the framework of special relativity. The numerical accuracy of the developed code is certified by several tests, in which we show comparisons with the corresponding analytical solutions. Using hydrodynamical data in our collapsar simulation, we estimate the annihilation rates in a post-processing manner. We show that the neutrino energy deposition and momentum transfers are strongest near the inner edge of the accretion disk. The beaming effects of special relativity are found to change the annihilation rates by several factors in the polar funnel region. After the accretion disk settles into a stationary state (typically later than ~9 s from the onset of gravitational collapse), we find that the neutrino-heating timescale in the vicinity of the polar funnel (lsim80 km) can become shorter than the hydrodynamical timescale, indicating that the neutrino-heated outflows can be launched there. We point out that the momentum transfer can play an important role as the energy deposition for the efficient acceleration of neutrino-driven outflows. Our results suggest that the neutrino pair annihilation has a potential importance equal to the conventional magnetohydrodynamic mechanism for igniting the GRB fireballs.
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