Study of Gamma-ray Bursts by the Cooperation with the Satellites and the Ground Based Observatories

我们研制了两种仪器，其主要目的是观测伽玛射线暴。一个是HETE-II（高能瞬态探测器II）卫星，另一个是MAXI（全天空X射线图像监视器）在国际空间站上。HETE-Ⅱ卫星于2000年10月9日发射升空，并成功进入预定轨道。我们从1997年就开始准备发射这颗卫星。对仪器的设计进行了改进，提高了仪器的检测效率和背景抑制效率。开展了多种环境试验或性能试验，在发射后的多次初始性能试验期间，获得了探测器在轨定标数据。现在我们开始正常观察。截至2001年3月26日，我们共发现了20个γ暴的候选事件，其中10个事件得到了其它观测的证实，并与HETE-Ⅱ卫星合作在宫崎大学大楼的屋顶上建立了光学跟踪观测系统。当HETE-II探测到伽玛暴时，它会向地面发送伽玛暴的位置信息。这些信息将很快通过互联网被计算机接收。然后，计算机控制系统开始使用小型望远镜进行跟踪观测。该系统所获得的数据将与以前获得的数据或编目数据进行比较。我们发现，用10秒左右的曝光时间，可以自动探测到亮度大于18等的未知天体，不仅研制了观测系统，而且分析了日本卫星的观测资料。我们在伽马射线爆发的X射线谱中发现了两个膝盖。这意味着伽玛射线暴的光谱变化的可能性。

We have developed two kinds of instrument whose prime purpose is observing the gamma-ray bursts. One is HETE-II (High Energy Transient Explorer II) satellite, the other is MAXI (Monitor of All sky X-ray Image) onboard international space station. HETE-II satellite was launched on October 9th 2000 and was successfully enterd into the orbit. We have prepared for launching this satellite since 1997. The design of the instrument was slightly changed to improve the detection efficiency and the background rejection efficiency than those of the former one which was failed to operate. Many kinds of environmental test or performance test were carried out.For the duration of many test for initial performance after its launch, we have obtained in-orbit calibration data of detectors. Now we have started the normal observation. As of March 26th 2001, 20 candidates for gamma-ray burst were discoverd and 10 events among them were confirmed by other observations.We have also constructed the optical follow-up observation system in cooperation with HETE-II satellite on the rooftop of the builing in Miyazaki university. When HETE-II discovers a gamma-ray burst, it sends the position information of gamma-ray burst to the ground. This information will be received by the computer through the internet soon. Then the conputer controls the system to start the follow-up observation using a small telescope. The obtained data by this system will be compared with one obtained previosly or the catalogued data. We found that we can detect automatically an unknown object brighter than 18th magnutude using the exposure about 10 seconds.We have not only developed an observational system, but also analized the observational data obtained by japanese satellite. We found two knees in the x-ray spectrum of a gamma-ray burst. This means the possibility of spectral variability of the gamma-ray burst.