Numerical Study of Gamma-Ray Burst Jet Formation in Collapsars
Numerical Study of Gamma-Ray Burst Jet Formation in Collapsars
复制标题
DOI：
10.1086/512057
复制
发表时间：
2006-08
期刊：
影响因子：
--
通讯作者：
S. Nagataki;R. Takahashi;A. Mizuta;T. Takiwaki
中科院分区：
文献类型：
--
作者：
S. Nagataki;R. Takahashi;A. Mizuta;T. Takiwaki
利用ZEUS-2D程序对产生伽玛暴喷流的崩塌星进行了二维MHD模拟，考虑了实际状态方程、中微子冷却和加热过程、磁场以及来自中心黑洞和自引力的引力。在这项研究中发现，中微子加热过程的效率不足以发射喷气式飞机。我们还发现，喷流主要是由B-ϕ场发射的，这些场被卷绕效应放大。然而，由于喷流中总能量相对于静止质量能量的比率并不是几百倍，我们得出的结论是，本研究中所看到的喷流不是伽玛暴喷流。这一结果表明，广义相对论效应对产生伽玛暴喷流很重要。此外，虽然需要用更长的物理时间(约10-100 S)来证实这一效应，但磁场吸积盘仍可能在发射伽玛暴喷流中发挥重要作用。结果表明，在吸积盘中合成了相当数量的56Ni。因此，吸积盘有可能提供足够的56Ni来解释超新星的光度。结果还表明，由于每个重子具有高熵的电子俘获而产生的富中子物质沿极轴被抛射。因此，有可能在这样的区域发生r-过程核合成。最后，许多中子将被喷出，这意味着来自中子衰变的信号可能被观察到为余辉或伽马射线的光曲线的延迟凸起。
Two-dimensional MHD simulations are performed using the ZEUS-2D code to investigate the dynamics of a collapsar that generates a GRB jet, taking account of realistic equation of state, neutrino cooling and heating processes, magnetic fields, and gravitational force from the central black hole and self-gravity. It is found that neutrino heating processes are not efficient enough to launch a jet in this study. It is also found that a jet is launched mainly by Bϕ fields that are amplified by the winding-up effect. However, since the ratio of total energy relative to the rest-mass energy in the jet is not as high as several hundred, we conclude that the jets seen in this study are not GRB jets. This result suggests that general relativistic effects will be important to generating a GRB jet. Also, the accretion disk with magnetic fields may still play an important role in launching a GRB jet, although a simulation for much longer physical time (~10-100 s) is required to confirm this effect. It is shown that a considerable amount of 56Ni is synthesized in the accretion disk. Thus, there will be a possibility for the accretion disk to supply the sufficient amount of 56Ni required to explain the luminosity of a hypernova. Also, it is shown that neutron-rich matter due to electron captures with high entropy per baryon is ejected along the polar axis. Thus, there will be a possibility that r-process nucleosynthesis occurs at such a region. Finally, many neutrons will be ejected from the jet, which suggests that signals from the neutron decays may be observed as the delayed bump of the light curve of the afterglow or gamma rays.