Intermittent mildly magnetized jets as the source of GRBs

Intermittent mildly magnetized jets as the source of GRBs
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间歇性轻度磁化射流作为伽马射线暴的来源

DOI：
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发表时间：
2021
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通讯作者：
E. Nakar
E. Nakar
中科院分区：
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文献类型：
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作者：
O. Gottlieb;O. Bromberg;A. Levinson;E. Nakar

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伽马射线暴（GRB）是由相对论喷流提供动力的，这种喷流在很宽的时间尺度上表现出不稳定性--从毫秒到秒。以前的数值研究表明，流体动力学（即，从可变发动机排出的（未磁化的）射流经受射流和茧状物质的强烈混合，这强烈抑制了GRB发射。在本文中，我们进行3D RMHD模拟的轻度磁化射流与功率调制持续时间为0.1秒和1秒，和一个稳定的磁场注入。我们发现，当喷流在发射场的磁化强度为$sigma sim 0.1$时，初始磁化强度被流中形成的激波放大到它强烈抑制重子加载的程度。我们估计，一个显着的污染可以避免，如果在注射的磁能构成至少百分之几的射流能量。的可变性时间尺度的射流后，它打破了星星，然后由注射周期，而不是由混合过程，这表明在实践中喷射喷射应波动的时间尺度短至10毫秒，以占所观察到的光变曲线。更好的稳定性被发现与较短的调制射流。我们的结论是，足够热的喷流，附近的光球的洛伦兹因子可以足够高，以允许有效的光球发射。我们的研究结果表明，喷流与10^{-2} < sigma < 1 $注入一个可变的发动机与$ sim 10 $ ms的占空比是合理的源长伽玛暴。
Gamma-ray bursts (GRBs) are powered by relativistic jets that exhibit intermittency over a broad range of timescales - from $ sim $ ms to seconds. Previous numerical studies have shown that hydrodynamic (i.e., unmagnetized) jets that are expelled from a variable engine are subject to strong mixing of jet and cocoon material, which strongly inhibits the GRB emission. In this paper we conduct 3D RMHD simulations of mildly magnetized jets with power modulation over durations of 0.1 s and 1 s, and a steady magnetic field at injection. We find that when the jet magnetization at the launching site is $sigma sim 0.1$, the initial magnetization is amplified by shocks formed in the flow to the point where it strongly suppresses baryon loading. We estimate that a significant contamination can be avoided if the magnetic energy at injection constitutes at least a few percent of the jet energy. The variability timescales of the jet after it breaks out of the star are then governed by the injection cycles rather than by the mixing process, suggesting that in practice jet injection should fluctuate on timescales as short as $ sim 10 $ ms in order to account for the observed light curves. Better stability is found for jets with shorter modulations. We conclude that for sufficiently hot jets, the Lorentz factor near the photosphere can be high enough to allow efficient photospheric emission. Our results imply that jets with $ 10^{-2} < sigma < 1 $ injected by a variable engine with $ sim 10 $ ms duty cycle are plausible sources of long GRBs.