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首页> 外文OA文献 >GRB 130925A: an ultralong gamma ray burst with a dust-echo afterglow, and implications for the origin of the ultralong GRBs
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GRB 130925A: an ultralong gamma ray burst with a dust-echo afterglow, and implications for the origin of the ultralong GRBs

机译：GRB 130925A：超长伽马射线爆发，伴有尘埃回响余辉，对超长GRB的起源有影响

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摘要

GRB 130925A was an unusual gamma ray burst (GRB), consisting of three distinct episodes of high-energy emission spanning ∼20 ks, making it a member of the proposed category of ‘ultralong’ bursts. It was also unusual in that its late-time X-ray emission observed by Swift was very soft, and showed a strong hard-to-soft spectral evolution with time. This evolution, rarely seen in GRB afterglows, can be well modelled as the dust-scattered echo of the prompt emission, with stringent limits on the contribution from the normal afterglow (i.e. external shock) emission. We consider and reject the possibility that GRB 130925A was some form of tidal disruption event, and instead show that if the circumburst density around GRB 130925A is low, the long duration of the burst and faint external shock emission are naturally explained. Indeed, we suggest that the ultralong GRBs as a class can be explained as those with low circumburst densities, such that the deceleration time (at which point the material ejected from the nascent black hole is decelerated by the circumburst medium) is ∼20 ks, as opposed to a few hundred seconds for the normal long GRBs. The increased deceleration radius means that more of the ejected shells can interact before reaching the external shock, naturally explaining both the increased duration of GRB 130925A, the duration of its prompt pulses, and the fainter-than-normal afterglow.
机译：GRB 130925A是不寻常的伽马射线爆发（GRB），由三个不同的高能发射事件组成，跨越约20kks，使其成为拟议的“超长”爆发类型的成员。同样不寻常的是，Swift观察到的其后期X射线发射非常柔和，并且随着时间的推移显示出从硬到弱的强烈光谱演化。在GRB余辉中很少见到的这种演变可以很好地建模为即时发射的尘埃散射回波，并对正常余辉（即外部冲击）发射的贡献进行严格限制。我们考虑并拒绝GRB 130925A是某种形式的潮汐破坏事件的可能性，而是表明，如果GRB 130925A周围的周向密度较低，则自然地解释了爆发的持续时间和微弱的外部冲击发射。确实，我们建议将超长GRB归类为具有低周向密度的GRB，这样，减速时间（此时从新生黑洞中喷射出来的物质被周向介质减速）约为20kks，而不是正常的长GRB的几百秒。减速半径的增加意味着更多的弹壳在受到外部冲击之前可以相互作用，这自然可以解释GRB 130925A的持续时间增加，其提示脉冲的持续时间以及暗淡的余辉。

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