伽马射线暴发动机超相对论磁动力喷流的模拟
Simulations of Ultrarelativistic Magnetodynamic Jets from Gamma-ray Burst Engines
摘要：
长持续时间的伽马射线暴（GRB）需要一个能够驱动等离子体射流的发动机，以达到高达几百的超相对论体洛伦兹因子和几度的窄张角。我们使用全球轴对称固定解决方案的磁主导（无力）超相对论性射流测试是否流行的磁驱动范式可以产生所需的洛伦兹因子和开度角。我们的全球解决方案是通过随时间变化的相对论性理想磁动力学数值模拟，从中央发动机的喷射超过六个数量级的半径。我们的模型主要是由黑洞或中子星旋转产生的喷流，然后通过一个巨大的恒星包层传播。我们发现，超新星爆发前恒星的大小和恒星内部压力的径向分布决定了喷流的终端洛伦兹因子和张角。在喷流从恒星爆发的半径处，我们动机良好的基准模型产生了洛伦兹因子$γ\sim 400$和半张角$θ_j\sim 2^\circ$，与许多长持续时间GRB的观测结果一致。其他一些参数略有不同的模型给出的$γ$在100到5000之间，$θ_j$在$0.1^\circ$到$10^\circ$之间，因此再现了伽玛射线暴喷流的推断性质范围。我们的一些解决方案的一个潜在的可观察到的特点是，在射流中的最大坡印廷通量被发现在$θ\sim θ_j$与射流功率集中在一个空心圆锥，而在洛伦兹因子的最大值发生在一个角度$θ$远小于$θ_j$也在一个空心圆锥。[删节]
英文摘要：
Long-duration gamma-ray bursts (GRBs) require an engine capable of driving a jet of plasma to ultrarelativistic bulk Lorentz factors of up to several hundred and into narrow opening angles of a few degrees. We use global axisymmetric stationary solutions of magnetically-dominated (force-free) ultrarelativistic jets to test whether the popular magnetic-driving paradigm can generate the required Lorentz factors and opening angles. Our global solutions are obtained via time-dependent relativistic ideal magnetodynamical numerical simulations which follow the jet from the central engine to beyond six orders of magnitude in radius. Our model is primarily motivated by the collapsar model, in which a jet is produced by a spinning black hole or neutron star and then propagates through a massive stellar envelope. We find that the size of the presupernova progenitor star and the radial profile of pressure inside the star determine the terminal Lorentz factor and opening angle of the jet. At the radius where the jet breaks out of the star, our well-motivated fiducial model generates a Lorentz factor $γ\sim 400$ and a half-opening angle $θ_j\sim 2^\circ$, consistent with observations of many long-duration GRBs. Other models with slightly different parameters give $γ$ in the range 100 to 5000 and $θ_j$ from $0.1^\circ$ to $10^\circ$, thus reproducing the range of properties inferred for GRB jets. A potentially observable feature of some of our solutions is that the maximum Poynting flux in the jet is found at $θ\sim θ_j$ with the jet power concentrated in a hollow cone, while the maximum in the Lorentz factor occurs at an angle $θ$ substantially smaller than $θ_j$ also in a hollow cone. [abridged]
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