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Numerical study of Gamma-Ray Bursts: Relativistic radiation hydrodynamics simulation.

机译：伽马射线爆发的数值研究：相对论辐射流体动力学模拟。

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摘要

Special relativistic physics plays an important role in many celestial phenomena such as Gamma-Ray Bursts (GRBs) and Active Galactic Nuclei (AGNs). During the past decade, many efforts have been made to simulate these phenomena by developing relativistic hydrodynamics codes with various algorithms. A realistic simulation needs to include magnetic field and radiation which makes the computational code more complicated. For my thesis research, I have developed a relativistic radiation hydrodynamics code in 3-D Cartesian coordinates. My code was developed by using PARAMESH, the Parallel Adaptive Mesh Refinement (AMR) library which makes my code run on parallel computers with AMR. My code is composed of two parts: relativistic hydrodynamics and radiation transport. For the hydrodynamics part, a Flux Corrected Transport (FCT) algorithm was used. I adopted the recent version of FCT algorithm called LCPFCT which was developed at Naval Research Lab to solve the 1-D Newtonian hydrodynamics equations in conservation form. Extension to 3-D was done using Zalesak's multi-dimensional limiter. According to previous results comparing various relativistic hydrodynamics codes based upon different algorithms, it is generally known that a relativistic hydrodynamics code developed with the FCT algorithm does not produce as accurate results as some other codes developed with high resolution shock capturing algorithms. However, the test problems simulated with my code show that the relativistic FCT code with a modification to the diffusion and antidiffusion coefficients is capable of producing results comparable to other algorithms when it is combined with AMR. The main advantage of using the FCT algorithm is its straightforward implementation when the code is extended to the relativistic radiation hydrodynamics regime because no Riemann solver is involved. For the radiation transport part of my code, I derived the governing equation of radiation transport in the comoving frame. The advantage of using the comoving frame equation is that the fundamental properties of radiation such as emissivity, absorption and scattering can be treated in the same way as when the fluid is at rest. The structure of the comoving frame equation is similar to that of the lab frame equation except that the comoving frame equation has additional terms for radiation intensity variation over angle and energy. The comoving frame equation is discretized by the implicit finite difference method and my radiation transport code solves the difference equation by using the Bi-CGSTAB method which iteratively solves linear systems of equations. The relativistic radiation hydrodynamics code is a combination of hydrodynamics and radiation transport with suitable micro-physics. At the current version of my code, an ideal gas equation of state with local thermal equilibrium (LTE) is assumed but various microphysics can be easily implemented into the code. In this dissertation, the equations to solve and the details of the code implementation are presented with a series of verification test problems. As for the astrophysical applications, I simulated the propagation of relativistic jets in the context of GRBs and AGNs with radiation included. The results show that radiation changes the morphology and dynamics of the jet in a significant way.
机译：相对论物理学在许多天体现象中发挥着重要作用，例如伽马射线爆发（GRB）和主动银河核（AGN）。在过去的十年中，通过使用各种算法开发相对论流体力学代码，人们已经做出了很多努力来模拟这些现象。现实的仿真需要包括磁场和辐射，这会使计算代码更加复杂。对于我的论文研究，我开发了一种在3D笛卡尔坐标系中的相对论辐射流体力学代码。我的代码是使用PARAMESH（并行自适应网格细化（AMR）库）开发的，该库使我的代码在具有AMR的并行计算机上运行。我的代码由两部分组成：相对论流体力学和辐射传输。对于流体动力学部分，使用了通量校正输运（FCT）算法。我采用了最新版本的FCT算法LCPFCT，该算法是由海军研究实验室开发的，用于以守恒形式求解一维牛顿流体动力学方程。使用Zalesak的多维限制器可以扩展到3-D。根据比较基于不同算法的各种相对论流体力学代码的先前结果，通常知道，使用FCT算法开发的相对论流体力学代码不会像使用高分辨率震动捕捉算法开发的某些其他代码那样产生准确的结果。但是，用我的代码模拟的测试问题表明，与扩散和反扩散系数修改的相对论性FCT代码与AMR结合使用时，能够产生与其他算法可比的结果。使用FCT算法的主要优点是，当代码扩展到相对论辐射流体动力学方案时，因为不涉及Riemann求解器，因此它的实现很简单。对于我的代码中的辐射传输部分，我导出了共同运动框架中辐射传输的控制方程。使用共同移动框架方程式的优势在于，可以像在流体静止时一样处理辐射的基本属性，例如发射率，吸收和散射。共同运动框架方程的结构与实验室框架方程的结构相似，不同之处在于共同运动框架方程具有辐射强度随角度和能量变化的附加项。共同运动的框架方程通过隐式有限差分法离散化，我的辐射传输代码通过使用Bi-CGSTAB方法迭代求解线性方程组来求解差分方程。相对论辐射流体力学代码是流体动力学和辐射传输与适当的微观物理学的结合。在我的代码的当前版本中，假设了具有局部热平衡（LTE）的理想气体状态方程，但是可以轻松地在代码中实现各种微观物理学。本文提出了要解决的方程式和代码实现的细节，并提出了一系列验证测试问题。至于天体物理应用，我模拟了相对论射流在包括辐射在内的GRB和AGN的情况下的传播。结果表明，辐射显着改变了射流的形态和动力学。

著录项

  • 作者

    Kwak, Kyujin.;

  • 作者单位

    State University of New York at Stony Brook.;

  • 授予单位 State University of New York at Stony Brook.;
  • 学科 Physics Astronomy and Astrophysics.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 129 p.
  • 总页数 129
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 天文学;
  • 关键词

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