Validation of radiative transfer computation with Monte Carlo method for ultra-relativistic background flow

JOURNAL OF COMPUTATIONAL PHYSICS

卷:348

Article

Ishii, Ayako^1,2  Ohnishi, Naofumi¹  Nagakura, Hiroki³  Ito, Hirotaka^4,5  Yamada, Shoichi⁶ 

[1] Tohoku Univ, Dept Aerosp Engn, Sendai, Miyagi 9808579, Japan

[2] Univ Tokyo, Sch Sci, Res Ctr Early Universe, Tokyo 1130033, Japan

[3] CALTECH, Walter Burke Inst Theoret Phys, TAPIR, Mailcode 350-17, Pasadena, CA 91125 USA

[4] RIKEN, Astrophys Big Bang Lab, Wako, Saitama 3510198, Japan

[5] RIKEN, Interdisciplinary Theoret Sci iTHES Res Grp, Wako, Saitama 3510198, Japan

[6] Waseda Univ, Adv Res Inst Sci & Engn, Tokyo 1698555, Japan

关键词: Gamma-ray burst;    Relativistic jet;    Radiative transfer;    Monte Carlo method;   

DOI  :  10.1016/j.jcp.2017.07.038

来源: Elsevier

【 摘 要 】

We developed a three-dimensional radiative transfer code for an ultra-relativistic background flow-field by using the Monte Carlo (MC) method in the context of gamma-ray burst (GRB) emission. For obtaining reliable simulation results in the coupled computation of MC radiation transport with relativistic hydrodynamics which can reproduce GRB emission, we validated radiative transfer computation in the ultra-relativistic regime and assessed the appropriate simulation conditions. The radiative transfer code was validated through two test calculations: (1) computing in different inertial frames and (2) computing in flow-fields with discontinuous and smeared shock fronts. The simulation results of the angular distribution and spectrum were compared among three different inertial frames and in good agreement with each other. If the time duration for updating the flow-field was sufficiently small to resolve a mean free path of a photon into ten steps, the results were thoroughly converged. The spectrum computed in the flow-field with a discontinuous shock front obeyed a power-law in frequency whose index was positive in the range from 1 to 10MeV. The number of photons in the high-energy side decreased with the smeared shock front because the photons were less scattered immediately behind the shock wave due to the small electron number density. The large optical depth near the shock front was needed for obtaining high-energy photons through bulk Compton scattering. Even one-dimensional structure of the shock wave could affect the results of radiation transport computation. Although we examined the effect of the shock structure on the emitted spectrum with a large number of cells, it is hard to employ so many computational cells per dimension in multi-dimensional simulations. Therefore, a further investigation with a smaller number of cells is required for obtaining realistic high-energy photons with multidimensional computations. (C) 2017 Elsevier Inc. All rights reserved.

【 授权许可】

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