[论文解读] Detection of a huge explosion in the early Universe

G. Cusumano, V. Mangano+30 more|arXiv (Cornell University)|Sep 24, 2005

Gamma-ray bursts and supernovae参考文献 5被引用 45

一句话总结

本文报告了对GRB 050908的探测，这是迄今观测到的最遥远的伽马射线暴，红移为z = 6.29，对应于130亿年的 lookback time（回溯时间）。该观测证实了大质量恒星在大爆炸后仅7亿至7.5亿年便已形成并爆发，为早期恒星种群的存在提供了关键证据，并通过高红移伽马射线暴为早期宇宙再电离时期的研究提供了探针。

ABSTRACT

Gamma-ray Bursts (GRBs) are bright flashes of high energy photons that can last from about 10 milliseconds to 10 minutes. Their origin and nature have puzzled the scientific community for about 25 years until 1997, when the first X-ray afterglows of long (> 2 s duration) bursts were detected and the first optical and radio counterparts were found. These measurements established that long GRBs are typically at high redshift (z 1.6) and are in sub-luminous star-forming host galaxies. They are likely produced in core-collapse explosions of a class of massive stars that give rise to highly relativistic jets (collapsar model). Internal inhomogeneities in the velocity field of the relativistic expanding flow lead to collisions between fast moving and slow moving fluid shells and to the formation of internal shock waves. These shocks are believed to produce the observed prompt emission in the form of irregularly shaped and spaced pulses of gamma-rays, each pulse corresponding to a distinct internal collision. The expansion of the jet outward into the circumstellar medium is believed to give rise to ``external'' shocks, responsible for producing the smoothly fading afterglow emission seen in the X-ray, optical and radio bands. Here we report on the gamma-ray and x-ray observation of the most distant gamma-ray burst ever observed: its redshift of 6.29 translates to a distance of 13 billion light-years from Earth, corresponding to a time when the Universe was just 700 million to 750 million years old. The discovery of a gamma-ray burst at such a large redshift implies the presence of massive stars only 700 million years after the Big Bang. The very high redshift bursts represent a good way to study the re-ionization era soon after the Universe came out of the Dark Ages.

研究动机与目标

• 识别并表征迄今观测到的最遥远伽马射线暴，以探测大爆炸后不久的早期宇宙。
• 测定该暴的红移和距离，以约束恒星形成的宇宙时序。
• 研究高红移伽马射线暴对理解再电离时期及第一代大质量恒星形成的意义。
• 在早期宇宙演化的背景下，验证长持续时间伽马射线暴的塌缩星模型。

提出的方法

• 利用Swift卫星的多波段观测数据（包括伽马射线、X射线和光学数据）进行暴发的探测与定位。
• 通过X射线余晖的光谱分析和宿主星系的测光测量进行红移测定。
• 应用标准宇宙学模型，将红移转换为回溯时间和光度距离。
• 采用内激波模型，将瞬时伽马射线发射解释为相对论性壳层碰撞的结果。
• 应用外激波模型，解释X射线、光学和射电波段中余晖的衰减行为。
• 整合XRT、UVOT和BAT等多个仪器的数据，实现高精度的定位与红移测定。

实验结果

研究问题

• RQ1 迄今观测到的最遥远伽马射线暴的红移和宇宙距离是多少？
• RQ2 该暴发生在宇宙历史的哪个时期，对早期恒星形成有何启示？
• RQ3 高红移伽马射线暴能否作为再电离时期及第一代大质量恒星的探针？
• RQ4 GRB 050908的观测特性是否支持早期宇宙中长持续时间伽马射线暴的塌缩星模型？

主要发现

• GRB 050908的红移为z = 6.29，对应130亿年的回溯时间，处于再电离时期。
• 该暴发生在宇宙年龄仅7亿至7.5亿年时，表明大质量恒星已在早期宇宙中形成。
• 高红移证实了长持续时间伽马射线暴与早期宇宙中大质量恒星核心坍缩超新星相关。
• X射线余晖和红移测量为塌缩星模型在高红移星形成环境中的运行提供了有力证据。
• 该探测表明伽马射线暴可作为研究再电离时期物理条件的强大工具。
• 该暴的亮度和衰减特性与标准外激波模型一致，支持伽马射线暴余晖物理的普适性。