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RISS 인기검색어
- 검색키워드
- 저자 : Shigehiro Nagataki (검색결과 3 건)
- 무료
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Neutrino Shadow and Explosion Mechanism of a Gamma-ray Burst
Rohta Takahashi,Shigehiro Nagataki 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4
Energy deposition due to neutrino pair annihilation around a neutrino-dominated accretion °ow (NDAF) and a black hole is one of the most signi.cant energy sources of a gamma-ray burst(GRB). We calculate the energy deposition rate (EDR) in a hyperaccreting disk around a Kerr black hole by solving the 3D general relativistic radiative transfer equations for neutrinos. We obtain the following results: (i) Most of the neutrinos comes from just outside the marginally bound orbit of neutrino, which means that light-bending eects should be included and 3D radiative transfer calculations are essential. (ii) The total EDR can be changed by 2 { 3 orders if the neutrino temperature changes by only a factor of 2, which means that the general relativistic calculation of neutrino emission processes in the ergosphere is very important. (iii) The local EDR can be increased by the black hole's rotation, even in the case when the rotational energy of the black hole cannot be eectively extracted.
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High Energy Neutrino Burst under the Internal Shock Model of Gamma-ray Bursts
Kohta Murase,Shigehiro Nagataki 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4
We calculate the proton cooling e±ciency including pion-multiplicity, and proton-inelasticity in photomeson production under the internal shock model of gamma-ray bursts (GRBs) by using the simulation kit GEANT4. We con.rm the validity of analytic approximate treatments based on GRB .ducial parameter sets, but also .nd that the eects of multiplicity and high inelasticity can be important for both proton cooling and the resulting spectra in some cases. We can estimate the maximum energy of accelerated protons in GRBs by considering various cooling processes. Using the obtained results, we can evaluate the neutrino °ux from one burst and a diuse neutrino background more quantitatively than past works. We assume that the GRB rate traces the star formation rate to obtain the diuse neutrino background. We also take into account the cooling processes of pions and muons, which are crucial to the resulting neutrino spectra. We introduce the nonthermal baryon-loading factor, rather than assume that GRBs are the main sources of ultra-high-enegy-cosmic-rays (UHECRs). We .nd that the obtained neutrino background can be comparable with the prediction of Waxman & Bahcall, although our ground in the estimation is dierent from theirs. This means su±cient photon density and accelerated protons may lead to the higher neutrino °ux, which may be di±cult to achieve. We study various parameters because there are many parameters in the model. The detection of high energy neutrinos from GRBs will provide a piece of strong evidences that protons are accelerated to very high energy in GRBs. Furthermore, the observations of a neutrino background has a possibility for not only testing the internal shock model of GRBs but also giving us infor- mation about the parameters in the model and about whether GRBs are sources of UHECRs or not.G
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A Neutrino-Cooled Accretion Disk as the Central Engine of Gamma-ray Bursts
Norita Kawanaka,Shin Mineshige,Shigehiro Nagataki 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4
It is often theoretically hypothesized that the enormous power released from gamma-ray bursts is generated by the accretion of a massive torus with approximately a solar mass onto a stellar-mass black hole. Such a torus (or disk) would become so dense and hot that the main cooling process would be neutrino radiation. We study the steady-state structure of this disk and consider the degeneracy of electrons and neutrinos, the opacity of neutrinos, and the equation of state of nuclear matter. The stability of the disk is also discussed.
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