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arXiv 1003.5916astro-ph.HE
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电子加速对伽马射线暴高能辐射的影响

Implications of electron acceleration for high-energy radiation from gamma-ray bursts

Rodolfo Barniol Duran, Pawan Kumar

摘要:

在最近的工作中,我们认为费米卫星从伽玛暴中探测到的能量大于100 MeV的光子是在具有弱磁场的外部前向激波中通过同步辐射产生的--这与激波压缩上游磁场为几十微高斯一致。在这里,我们研究电子是否可以被加速到这样的能量,使他们辐射同步辐射光子的能量高达约10 GeV,在这个特定的情况下。我们使用两种方法来做到这一点:(i)我们检查这些电子是否可以被限制在激波前沿;(ii)我们计算它们被加速时的辐射损失。我们发现,这些电子仍然局限于冲击波前,只要上游的磁场是>~ 10微高斯,并没有遭受实质性的辐射损失,唯一的条件是,外部的反向冲击辐射是不是太亮:峰值通量小于1焦耳,以产生光子的100兆电子伏,小于~100毫焦耳,以产生1-GeV的光子。我们还发现,在100兆电子伏辐射的电子的加速时间是几秒钟(在观察者框架),和加速时间是在几个GeV辐射的电子有点长。这可以解释费米卫星报告的长伽马射线暴触发时间后的最初几秒内缺乏>100 MeV的光子,以及GeV和100 MeV能量的光子之间的轻微滞后。在这种情况下,我们模拟了外部前向冲击光变曲线的发生,发现它与GRB 080916 C和类似爆发的100 MeV光变曲线中观察到的急剧上升一致。

英文摘要:

In recent work we suggested that photons of energy >100 MeV detected from GRBs by the Fermi Satellite are produced via synchrotron emission in the external forward shock with a weak magnetic field - consistent with shock compressed upstream magnetic field of a few tens of micro-Gauss. Here we investigate whether electrons can be accelerated to energies such that they radiate synchrotron photons with energy up to about 10 GeV in this particular scenario. We do this using two methods: (i) we check if these electrons can be confined to the shock front; and (ii) we calculate radiative losses while they are being accelerated. We find that these electrons remain confined to the shock front, as long as the upstream magnetic field is >~ 10 micro-Gauss, and don't suffer substantial radiative losses, the only condition required is that the external reverse shock emission be not too bright: peak flux less than 1 Jy in order to produce photons of 100 MeV, and less than ~100 mJy for producing 1-GeV photons. We also find that the acceleration time for electrons radiating at 100 MeV is a few seconds (in observer frame), and the acceleration time is somewhat longer for electrons radiating at a few GeV. This could explain the lack of >100 MeV photons for the first few seconds after the trigger time for long GRBs reported by the Fermi Satellite, and also the slight lag between photons of GeV and 100 MeV energies. We model the onset of the external forward shock light curve in this scenario and find it consistent with the sharp rise observed in the 100-MeV light curve of GRB080916C and similar bursts.

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