A REVISED LIMIT OF THE LORENTZ FACTORS OF GAMMA-RAY BURSTs WITH TWO EMITTING REGIONS
A REVISED LIMIT OF THE LORENTZ FACTORS OF GAMMA-RAY BURSTs WITH TWO EMITTING REGIONS
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DOI：
10.1088/2041-8205/726/1/l2
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发表时间：
2010-08
期刊：
影响因子：
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通讯作者：
Y. Zou;Yizhong Fan;T. Piran
中科院分区：
文献类型：
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作者：
Y. Zou;Yizhong Fan;T. Piran
对伽马射线暴(GRBs)GeV辐射的费米观测表明，有些伽马射线暴的洛伦兹因子约为1000，甚至更高。与此同时，同样的费米观测也显示出扩展的GeV发射，这表明这种较高的能量发射可能是余辉的一部分，它与较低能量的瞬时发射不来自同一区域。如果这种解释是正确的，那么我们可能不得不重新考虑基于单区模型的洛伦兹因子的不透明度限制。在这里我们描述了一个两区模型，其中GeV光子的发射半径比MeV光子的半径大，并计算了GeV光子通过低能光子壳层产生对的光学厚度。我们发现，正如预期的那样，洛伦兹因子的新的两区限制要低得多。当应用于费米爆发时，与单区模型相比，相应的极限降低了五倍。MeV和GeV区域可能都有相对适中的洛伦兹因子(∼200-400)。这两个区域的限制比一个区域的限制要软得多。
Fermi observations of GeV emission from gamma-ray bursts (GRBs) have suggested that the Lorentz factor of some GRBs is around a thousand or even higher. At the same time, the same Fermi observations have shown an extended GeV emission indicating that this higher energy emission might be a part of the afterglow and it does not come from the same region as the lower energy prompt emission. If this interpretation is correct then we may have to reconsider the opacity limits on the Lorentz factor which are based on a one-zone model. We describe here a two-zone model in which the GeV photons are emitted in a larger radius than the MeV photons and we calculate the optical depth for pair creation of a GeV photon passing the lower energy photons shell. We find that, as expected, the new two-zone limits on the Lorentz factor are significantly lower. When applied to Fermi bursts the corresponding limits are lower by a factor of five compared to the one-zone model. It is possible that both the MeV and GeV regions have relatively modest Lorentz factors (∼200–400). This two-zone limit is significantly softer than the one-zone limit.