Is GeV emission from Gamma-Ray Bursts of external shock origin?
Is GeV emission from Gamma-Ray Bursts of external shock origin?
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DOI：
10.1111/j.1365-2966.2011.18648.x
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发表时间：
2010-12
影响因子：
4.8
通讯作者：
A. Maxham;Bin-Bin Zhang-Bin;Bing Zhang
中科院分区：
文献类型：
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作者：
A. Maxham;Bin-Bin Zhang-Bin;Bing Zhang
最近费米大面积望远镜（LAT）对伽马射线暴（GRB）的观测显示，高能辐射（100 MeV以上）具有幂律衰减特征，这导致了它起源于外部冲击的建议。我们分析了四个伽玛暴（080916 C，090510，090902 B和090926 A）联合检测费米LAT和伽玛暴监测器（GBM），这在两个仪器的能量波段具有高质量的光变曲线。使用MeV瞬时排放（GBM）数据，我们可以记录中央发动机输出的能量随时间的变化。假设一个恒定的辐射效率，我们能够跟踪能量积累的外部冲击，使用我们的内部/外部壳模型代码。通过求解绝热和辐射冲击波的早期演化，我们计算了LAT波段的高能发射光变曲线，并将其与每次爆发的观测结果进行了比较。该模型能较好地拟合T90以后的后期LAT光变曲线.然而，由于连续的能量注入到爆炸波在即时发射阶段，早期的外部冲击发射不能解释所观察到的GeV通量水平。在瞬发阶段（T 90之前）的高能发射很可能是一个逐渐增强的外部冲击分量和一个主导的发射分量，这是一个内部的起源的叠加。
Recent observations of Gamma-Ray Bursts (GRBs) by the Fermi Large Area Telescope (LAT) revealed a power-law decay feature of the high-energy emission (above 100 MeV), which led to the suggestion that it originates from an external shock. We analyse four GRBs (080916C, 090510,090902B and 090926A) jointly detected by Fermi LAT and Gamma-ray Burst Monitor (GBM), which have high-quality light curves in both instrument energy bands. Using the MeV prompt emission (GBM) data, we can record the energy output from the central engine as a function of time. Assuming a constant radiative efficiency, we are able to track energy accumulation in the external shock using our internal/external shell model code. By solving for the early evolution of both an adiabatic and a radiative blastwave, we calculate the high-energy emission light curve in the LAT band and compare it with the observed one for each burst. The late time LAT light curves after T 90 can be well fitted by the model. However, due to continuous energy injection into the blastwave during the prompt emission phase, the early external shock emission cannot account for the observed GeV flux level. The high-energy emission during the prompt phase (before T 90 ) is most likely a superposition of a gradually enhancing external shock component and a dominant emission component that is of an internal origin.