标题： 极亮伽马射线暴 GRB 080916C 的红移及其余辉 显示英文标题

标题： The redshift and afterglow of the extremely energetic gamma-ray burst GRB 080916C

摘要： 来自伽马射线暴（GRBs）的GeV光子探测对于这些最具能量的宇宙爆炸的解释和建模具有重要意义。 然而，充分利用高能测量结果依赖于对事件距离的精确了解。 在这里，我们报告了由费米伽马射线空间望远镜以显著高能光子（>0.1 GeV）检测到的第一个GRB 080916C的余辉发现及其随后的红移测定。 观测使用了位于ESO 2.2米望远镜上的七通道成像仪GROND、南非Nagoya-SAAO 1.4米望远镜上的SIRIUS仪器以及双子座南望远镜上的GMOS仪器。 基于伽玛射线光学和近红外探测器（GROND）同时进行的7滤波器观测得到的余辉测光红移z=4.35±0.15，将GRB 080916C列为最遥远的GRBs中的前5%，使其成为迄今为止已知的最强大的GRB。 从如此遥远的事件中检测到GeV光子相当令人惊讶。 在暴发辐射期间观察到的伽马射线变化与红移一起表明超相对论喷流的洛伦兹因子的下限为Gamma > 1090。 这一数值与GRB中任何先前的Gamma测量值相媲美，并增强了GRB 080916C的极端性质。 显示英文摘要

摘要： The detection of GeV photons from gamma-ray bursts (GRBs) has important consequences for the interpretation and modelling of these most-energetic cosmological explosions. The full exploitation of the high-energy measurements relies, however, on the accurate knowledge of the distance to the events. Here we report on the discovery of the afterglow and subsequent redshift determination of GRB 080916C, the first GRB detected by the Fermi Gamma-Ray Space Telescope with high significance detection of photons at >0.1 GeV. Observations were done with 7-channel imager GROND at the 2.2m MPI/ESO telescope, the SIRIUS instrument at the Nagoya-SAAO 1.4m telescope in South Africa, and the GMOS instrument at Gemini-S. The afterglow photometric redshift of z=4.35+-0.15, based on simultaneous 7-filter observations with the Gamma-Ray Optical and Near-infrared Detector (GROND), places GRB 080916C among the top 5% most distant GRBs, and makes it the most energetic GRB known to date. The detection of GeV photons from such a distant event is rather surprising. The observed gamma-ray variability in the prompt emission together with the redshift suggests a lower limit for the Lorentz factor of the ultra-relativistic ejecta of Gamma > 1090. This value rivals any previous measurements of Gamma in GRBs and strengthens the extreme nature of GRB 080916C.