Observational Study of the Cosmic X-ray Background with the Scientifica Satellite ASTRO-D

这个科学项目的目的是利用1993年2月20日发射的科学卫星ASTRO-D （ASCA）调查宇宙x射线背景（CXB），并对ASCA上的GIS（气体成像光谱仪）仪器进行在轨校准。CXB是一种神秘的现象，在x射线天文学诞生之初就被科学界所知，但它的确切起源仍然未知。经过三年的调研，取得了以下成果：完成了系统的在轨性能验证和详细标定。特别是，GIS粒子背景已被精确量化，这对包括CXB.2在内的漫射辐射的研究是重要的。考虑到x射线望远镜的点扩散函数和杂散光，提出了一种适用于大范围x射线源的数据分析新方案。对于各种可能对CXB有贡献的银河系外物体，我们获得了新的见解。特别地；(1)揭示了大尺度磁场的重要性；(2)发现暗物质分布具有星系/星系团的层次性；(3)在邻近的正常星系中发现了一些低光度的活动核。在1-10 keV能量范围内，CXB光谱显示出单一的幂律形状，光子指数为1.4。这与以前用ROSAT卫星获得的结果相矛盾。此外，在去除亮度大于3*10^<-13> erg/s/cm^2 （2-10 keV）的点源后，证实了CXB表面亮度的场间波动不超过<正负>3%。这些结果给试图将CXB合成为遥远天体叠加的模型提供了强有力的约束。

The objective of this scientific project is to investigate the cosmic X-ray background (CXB), using the scientific satellite ASTRO-D (ASCA) launched on 1993 February 20, and to carry out in-orbit calibration of the GIS (Gas Imaging Spectrometer) instrument onboard ASCA.The CXB is anenigmatic phenomenon known science the birth of the X-ray astronomy, but its exact origin is still unknown. Through three years of investigation, the following achievements have been obtained.1. The in-orbit performance verification and detailed calibration of the GIS have been accomplished. In particular, the GIS particle background has been precisely quantified, which is important for the investigation of diffuse emissions including the CXB.2. By taking into account the point spread function and stray light of the X-ray telescope, a new scheme of data analysis has been developed for application to widely extended X-ray sources.3. New insight has been obtained for various extra-Galactic objects which potentially contribute to the CXB.In particular ; (1) importance of the large-scale magnetic fields has been revealed ; (2) the dark matter distribution has been found to exhibit galaxy/cluster tierarchy ; and (3) a number of low-luminosity active nuclei have been discovered in nearby normal galaxies.4. The CXB spectrum has been show to exhibit a single power-law shape with a photon index 1.4 over the 1-10 keV energy range. This contradicts the previous results obtained with the ROSAT satellite. In addition, after removing point sources brighter than 3*10^<-13> erg/s/cm^2 (in 2-10 keV), the field-to field fluctuation of te CXB surface brightness is confirmed to be <plus-minus>3% at most. These results give strong constraints to the models that attempt to synthesize the CXB as a superposition of distant objects.