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arXiv 1307.2663astro-ph.HE
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关于伽马射线暴中GeV发射的起源

On the origin of GeV emission in gamma-ray bursts

Andrei M. Beloborodov, Romain Hascoet, Indrek Vurm

摘要:

伽马射线暴(GRB)最常见的前身是具有强烈星风的大质量恒星。我们表明,在风中的GRB冲击波应该发出一个明亮的GeV闪光。它是由前向冲击波后面的热等离子体的逆康普顿冷却产生的。闪光的主要部分是由瞬时MeV辐射(以较小半径发射)的散射形成的,这些辐射穿过外部爆炸波。逆康普顿闪光是明亮的,由于外部介质的巨大e+富集。在后期,冲击波切换到正常的同步加速器自康普顿冷却。详细的传输模拟证明了该机制。所观察到的即时MeV辐射作为模拟的输入,我们使用GRB 080916 C作为一个例子。结果再现了费米望远镜观测到的GeV闪光。它解释了延迟的启动,陡峭的上升,峰值流量,峰值的时间,长的平稳下降,和GeV的发射光谱斜率。重现所有这些特征所需的风密度是沃尔夫-拉叶星的典型特征。我们的模拟预测强烈的TeV发射1分钟后,爆发触发,然后在所观察到的高能光谱截止预期从河外背景光的吸收。此外,一个明亮的光学对应的GeV闪光的预测合理的值的磁场,这样的双(光学+GeV)闪光已被观察到GRB 130427 A。

英文摘要:

The most common progenitors of gamma-ray bursts (GRBs) are massive stars with strong stellar winds. We show that the GRB blast wave in the wind should emit a bright GeV flash. It is produced by inverse Compton cooling of the thermal plasma behind the forward shock wave. The main part of the flash is shaped by scattering of the prompt MeV radiation (emitted at smaller radii) which streams through the external blast wave. The inverse-Compton flash is bright due to the huge e+- enrichment of the external medium. At late times, the blast wave switches to normal synchrotron-self-Compton cooling. The mechanism is demonstrated by a detailed transfer simulation. The observed prompt MeV radiation is taken as an input of the simulation; we use GRB 080916C as an example. The result reproduces the GeV flash observed by the Fermi telescope. It explains the delayed onset, the steep rise, the peak flux, the time of the peak, the long smooth decline, and the spectral slope of GeV emission. The wind density required to reproduce all these features is typical of Wolf-Rayet stars. Our simulation predicts strong TeV emission 1 min after the burst trigger; then a cutoff in the observed high-energy spectrum is expected from absorption by extragalactic background light. In addition, a bright optical counterpart of the GeV flash is predicted for plausible values of the magnetic field; such a double (optical+GeV) flash has been observed in GRB 130427A.

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