Study of the formation and the evolution of the Universe with prompt observations of gamma-ray bursts

本研究的目的是通过对早期光学余辉和近红外余辉的快速观测，探讨伽玛射线暴（GRBs）中相对论性喷流的产生机制和古代宇宙中大质量恒星形成的历史。我们成功地用斯巴鲁望远镜测量了GRB 050904余辉的光谱。我们发现，这是有记录以来距离最远的伽马射线暴，红移为6.3，也就是128亿年前，宇宙在那个年代基本上是电离的，我们还测量了宿主星系的金属丰度。我们建造了两台50厘米的光学望远镜，配有专门设计的三色相机。这两个望远镜自动响应卫星发出的GRB警报，对GRB余辉进行观测。获取的图像被自动分析并存储在数据库中。例如，GRB 060115的余辉首先在冈山成像，并由国外团队领导红移测量（z=3.5）。我们还将冈山现有的91厘米望远镜改装成一个自动近红外望远镜，视野非常宽。此外，我们在石岛天文台的1米望远镜上安装了三色相机，以增加观测机会。作为向快速通知grb位置的小卫星迈出的第一步，我们开发了一种使用APD的轻型辐射探测器，我们将其安装在学生建造的非常小的卫星“可爱1.7+APD”上。2006年2月，这颗卫星被JAXA的M-V - 8火箭成功地搭载到轨道上，但由于卫星通信系统出现故障，未能获得探测器的数据。2008年4月，我们发射了第二颗卫星“可爱1.7+APD II”，通过测量辐射区内的低能带电粒子，成功地对APD辐射探测器进行了首次在轨验证。

The goal of this study is to investigate the production mechanism of the relativistic jets in gamma-ray bursts (GRBs) and the history of the massive star formation in the ancient Universe using GRBs by prompt observations of early optical and near-infrared afterglows. We succeeded in measuring the optical spectrum of the afterglow of GRB 050904 with the Subaru Telescope. We found that it was the most distant gamma-ray burst ever recorded, at a redshift of 6.3, or 12.8 billion years ago, and that the Universe was largely ionized at that age, and measured the metallicity of the host galaxy. We built two 50cm optical telescopes equipped with specially designed tricolor cameras. These two telescopes respond automatically to the GRB alerts from the satellites to perform observations of the GRB afterglows. The obtained images are automatically analyzed and stored in the database. As an example, the afterglow of GRB 060115 was imaged at Okayama first, and led the redshift measurement (z=3.5) by a foreign team. We also modified the existing 91cm telescope in Okayama into an automatic near-infrared telescope with a very wide field of view. Furthermore, we installed our tri-color camera on the 1-m telescope at the Ishigakijima Observatory to increase the observing opportunities.As a first step towards a small satellite that promptly notifies the location of GRBs, we developed a light-weight radiation detector using APDs, which we mounted on the student-built very small satellite "Cute 1.7+APD". The satellite was successfully launched into an orbit as a piggy back payload with the JAXA M-V 8 rocket in February 2006, but the data of the detector was not obtained due to a trouble in the communication system of the satellite. With the second satellite "Cute 1.7+APD II" launched in April 2008, we succeeded in the first in-orbit verification of radiation detector using APDs by measuring the low-energy charged particles in the radiation zone.