GRB110920A的极窄光谱：局部次光球耗散的进一步证据
Extremely narrow spectrum of GRB110920A: further evidence for localised, subphotospheric dissipation
摘要：
大量的证据表明，相对论外流中的光球在形成观测到的MeV谱中起着重要的作用。然而，目前尚不清楚光谱是否完全由光球层产生，或者光谱的实质部分是否是由远在光球层之上的过程添加的。本文详细研究了GRB 110920 A单脉冲的$γ-$射线辐射，它的光谱在接近爆发末端时变得非常窄。我们表明，发射可以被解释为康普顿热光子冷电子在未磁化流出的光学深度为$τ\sim 20$。电子通过在饱和半径附近发生的局部耗散来接收能量。GRB 110920 A的主要光谱成分及其演变，因此，在这种解释中，充分解释了来自光球的发射，包括在高光学深度的局部耗散。
英文摘要：
Much evidence points towards that the photosphere in the relativistic outflow in GRBs plays an important role in shaping the observed MeV spectrum. However, it is unclear whether the spectrum is fully produced by the photosphere or whether a substantial part of the spectrum is added by processes far above the photosphere. Here we make a detailed study of the $γ-$ray emission from single pulse GRB110920A which has a spectrum that becomes extremely narrow towards the end of the burst. We show that the emission can be interpreted as Comptonisation of thermal photons by cold electrons in an unmagnetised outflow at an optical depth of $τ\sim 20$. The electrons receive their energy by a local dissipation occurring close to the saturation radius. The main spectral component of GRB110920A and its evolution is thus, in this interpretation, fully explained by the emission from the photosphere including localised dissipation at high optical depths.
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