Signs of magnetic acceleration and multizone emission in GRB 080825C
Signs of magnetic acceleration and multizone emission in GRB 080825C
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DOI：
10.1093/mnras/stw432
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发表时间：
2016-02
影响因子：
4.8
通讯作者：
E. Moretti;M. Axelsson
中科院分区：
文献类型：
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作者：
E. Moretti;M. Axelsson
用费米伽马射线空间望远镜研究伽马射线爆发的主要结果之一是证实了能谱中可能存在几种发射成分。在这里，我们重新分析GRB 080825 C的光谱使用费米大面积望远镜（LAT）和伽玛射线暴监测仪器的数据。虽然相当微弱，但它是费米-LAT探测到的第一个伽马射线暴。我们通过使用LAT低能量事件覆盖30-100兆电子伏波段的原始分析进行改进。我们发现在四个时间仓中的两个时间仓中，在主发射峰（使用带函数建模）上方存在显著性为3.5σ的额外分量的证据。该组件是很好地拟合普朗克函数，但显示出不寻常的行为：峰值能量增加，在即时发射阶段，达到几个兆电子伏的能量。这是第一次看到这种趋势，意味着这种成分的来源与以前检测到的不同。我们认为，这两个光谱分量可能出现在不同地区的外流，并假设其中一个起源于光球，可以实现强约束。最有希望的模型似乎是，高能量峰值是光球发射的结果，在坡印亭通量占主导地位的流出，磁化随时间增加。
One of the major results from the study of gamma-ray bursts with the Fermi Gamma-ray Space Telescope has been the confirmation that several emission components can be present in the energy spectrum. Here, we reanalyse the spectrum of GRB 080825C using data from the Fermi-Large Area Telescope (LAT) and Gamma-ray Burst Monitor instruments. Although fairly weak, it is the first gamma-ray burst detected by the Fermi-LAT. We improve on the original analysis by using the LAT Low Energy events covering the 30–100 MeV band. We find evidence of an additional component above the main emission peak (modelled using a Band function) with a significance of 3.5σ in two out of the four time bins. The component is well fitted by a Planck function, but shows unusual behaviour: the peak energy increases in the prompt emission phase, reaching energies of several MeV. This is the first time such a trend has been seen, and implies that the origin of this component is different from those previously detected. We suggest that the two spectral components likely arise in different regions of the outflow, and that strong constraints can be achieved by assuming one of them originates from the photosphere. The most promising model appears to be that the high-energy peak is the result of photospheric emission in a Poynting flux dominated outflow where the magnetization increases with time.