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arXiv 1204.0261astro-ph.HE
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星周壳层中的伽马射线暴:耀斑的一种可能解释

Gamma-Ray Bursts in Circumstellar Shells: A Possible Explanation for Flares

Robert A. Mesler, Daniel J. Whalen, Nicole M. Lloyd-Ronning, Chris L. Fryer, Ylva M. Pihlström

摘要:

现在普遍认为,长持续时间的伽马射线暴(GRB)是由于大质量旋转恒星的坍缩。然而,精确的崩溃过程本身尚未完全理解。强风、爆发和强烈的电离紫外线辐射来自单颗恒星或强相互作用的双星,预计会摧毁产生它们的分子云核心,并为爆炸创造高度复杂的环暴环境。这样的环境可能会在伽玛射线暴的光变曲线上留下独特的印记,以确定其前身的性质及其坍缩。我们已经进行了数值模拟的现实环境中的各种长持续时间的伽玛暴祖与ZEUS-MP,并已开发出一种分析方法来计算这些配置文件中的伽玛暴光变曲线。虽然一个完整的,三维的,相对论性磁流体动力学计算模型,需要精确地描述在复杂的环境中从伽玛射线暴的光变曲线,我们的方法可以提供一个定性的理解这些现象。我们发现,在标准余辉模型的背景下,大规模的壳周围的伽玛射线暴产生强烈的签名,在他们的光变曲线,这可以区分他们从那些发生在均匀介质或稳定的风。这些特征可以约束壳体的质量和弹射前后的风的性质。此外,GRB与环暴壳的相互作用被认为产生与观察到的X射线耀斑相一致的特征,X射线耀斑通常归因于中央发动机的延迟能量注入。我们的算法计算光变曲线也适用于伽玛暴在各种环境中,如在高红移宇宙晕或原星系,这两者都将很快成为未来的调查,如JANUS或龙虾的目标。

英文摘要:

It is now generally accepted that long-duration gamma ray bursts (GRBs) are due to the collapse of massive rotating stars. The precise collapse process itself, however, is not yet fully understood. Strong winds, outbursts, and intense ionizing UV radiation from single stars or strongly interacting binaries are expected to destroy the molecular cloud cores that give birth to them and create highly complex circumburst environments for the explosion. Such environments might imprint features on GRB light curves that uniquely identify the nature of the progenitor and its collapse. We have performed numerical simulations of realistic environments for a variety of long-duration GRB progenitors with ZEUS-MP, and have developed an analytical method for calculating GRB light curves in these profiles. Though a full, three-dimensional, relativistic magnetohydrodynamical computational model is required to precisely describe the light curve from a GRB in complex environments, our method can provide a qualitative understanding of these phenomena. We find that, in the context of the standard afterglow model, massive shells around GRBs produce strong signatures in their light curves, and that this can distinguish them from those occurring in uniform media or steady winds. These features can constrain the mass of the shell and the properties of the wind before and after the ejection. Moreover, the interaction of the GRB with the circumburst shell is seen to produce features that are consistent with observed X-ray flares that are often attributed to delayed energy injection by the central engine. Our algorithm for computing light curves is also applicable to GRBs in a variety of environments such as those in high-redshift cosmological halos or protogalaxies, both of which will soon be targets of future surveys such as JANUS or Lobster.

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