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arXiv 1801.06124astro-ph.HE
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提示gamma-ray发射与GW 170817相关的GRB 170817 A:一致的图片

Prompt gamma-ray emission of GRB 170817A associated to GW 170817: A consistent picture

Houri Ziaeepour

摘要:

与第一次探测到来自双中子星(BNS)合并的引力波有关的短GRB 170817 A在许多方面都是不寻常的。可能的解释是从茧或茧破裂,离轴的结构或均匀射流,和轴上的超相对论性喷流与密度和洛伦兹因子减少的排放。本文利用激波演化和同步辐射/自康普顿辐射的唯象模型模拟了GRB 170817 A的瞬发辐射,并对上述建议进行了验证。我们发现,同步辐射从一个温和的相对论性茧与洛伦兹因子2-3,在文献中考虑,产生太软,太长,太亮的提示发射。洛伦兹因子约为10的结构射流的离轴视图可以再现观测结果,但需要将动能非常有效地传递到内部冲击中的电子,这是粒子模拟所不赞成的。我们还评论了作为产生瞬发γ射线的一种机制的破茧。一个相对论性喷流的洛伦兹因子约为100,密度低于典型的短伽玛暴似乎是最合理的模型,我们得出结论,伽玛暴170817 A是本质上暗淡。基于这一结果和文献中BNS合并的相对论磁流体力学模拟结果,我们讨论了可能导致这种微弱短伽玛暴的物理和天文条件。我们发现,小的质量差的祖先中子星,他们的年龄和减少磁场,和反对齐的自旋轨道角动量诱导的环境引力扰动的寿命期间的BNS作为GRB 170817 A的昏暗的原因。我们预测,在较低的红移BNS合并产生平均较暗的伽玛暴。

英文摘要:

The short GRB 170817A associated to the first detection of gravitation waves from a Binary Neutron Star (BNS) merger was in many ways unusual. Possible explanations are emission from a cocoon or cocoon break out, off-axis view of a structured or uniform jet, and on-axis ultra-relativistic jet with reduced density and Lorentz factor. Here we use a phenomenological model of shock evolution and synchrotron/self-Compton emission to simulate the prompt emission of GRB 170817A and to test above proposals. We find that synchrotron emission from a mildly relativistic cocoon with a Lorentz factor of 2-3, as considered in the literature, generates a too soft, too long, and too bright prompt emission. Off-axis view of an structured jet with a Lorentz factor of about 10 can reproduce observations, but needs a very efficient transfer of kinetic energy to electrons in internal shocks, which is disfavored by particle in cell simulations. We also comment on cocoon breakout as a mechanism for generation of the prompt gamma-ray. A relativistic jet with a Lorentz factor of about 100 and a density lower than typical short GRBs seems to be the most plausible model and we conclude that GRB 170817A was intrinsically faint. Based on this result and findings of relativistic magnetohydrodynamics simulations of BNS merger in the literature we discuss physical and astronomical conditions, which may lead to such faint short GRBs. We identify small mass difference of progenitor neutron stars, their old age and reduced magnetic field, and anti-alignment of spin-orbit angular momentum induced by environmental gravitational disturbances during the lifetime of the BNS as causes for the faintness of GRB 170817A. We predict that BNS mergers at lower redshifts generate on average fainter GRBs.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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