Efficiency Crisis of Swift Gamma-Ray Bursts with Shallow X-ray Afterglows : Prior Activity or Time-Dependent Microphysics?
Efficiency Crisis of Swift Gamma-Ray Bursts with Shallow X-ray Afterglows : Prior Activity or Time-Dependent Microphysics?
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DOI：
10.1051/0004-6361:20064939
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发表时间：
2005-11
影响因子：
6.5
通讯作者：
K. Ioka;K. Toma;R. Yamazaki;Takashi Nakamura
中科院分区：
文献类型：
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作者：
K. Ioka;K. Toma;R. Yamazaki;Takashi Nakamura
背景。雨燕卫星观测到的伽玛射线暴（GRBs）的大多数x射线余辉在最初几个小时内都有一个浅衰减阶段$\propto$$t^{-1/2}$。目标。这是标准的余辉模型无法预测的，需要解释。方法。我们讨论了浅层衰变需要一个不合理的高伽马射线效率，$\ga$$75{-}90\%$，在目前的模型中，这是很难由内部冲击产生的。如果弱相对论性爆炸发生在主爆炸之前$10^3{-}10^6$ s，或者如果电子能量的微物理参数在浅层衰变期间增加$\epsilon_{\rm e} \propto t^{1/2}$，则可以避免这种危机。前一种解释预测了一个非常长的前体，而两种解释都倾向于来自反向冲击的微弱光学闪光，正如最近报道的那样。我们还计算了多波长余辉，并与观测结果进行了比较。结果。在浅x射线衰变结束时没有光学断裂表明更倾向于具有额外衰减磁场的时间相关微物理模型，$\epsilon_B \propto t^{-0.6}$。
Context. Most X-ray afterglows of gamma-ray bursts (GRBs) observed by the Swift satellite have a shallow decay phase $\propto$$t^{-1/2}$ in the first few hours. Aims. This is not predicted by the standard afterglow model and needs an explanation. Methods. We discuss that the shallow decay requires an unreasonably high gamma-ray efficiency, $\ga$$75{-}90\%$, within current models, which is difficult to produce by internal shocks. Such a crisis may be avoided if a weak relativistic explosion occurs ~$10^3{-}10^6$ s prior to the main burst or if the microphysical parameter of the electron energy increases during the shallow decay, $\epsilon_{\rm e} \propto t^{1/2}$. The former explanation predicts a very long precursor, while both prefer dim optical flashes from the reverse shock, as was recently reported. We also calculate the multi-wavelength afterglows and compare them with observations. Results. No optical break at the end of the shallow X-ray decay indicates a preference for the time-dependent microphysics model with additionally decaying magnetic fields, $\epsilon_B \propto t^{-0.6}$.