Development of Image Reconstruction Methods for a Hard X-ray Telescope of the Fourier-Synthesis Type

本项目的目的是开发傅里叶合成型硬x射线图像的图像重建方法，特别是用于SOLAR-A（“Yohkoh”）卫星上的硬x射线望远镜（HXT），并在工作站构建图像分析系统。1990年，我们编写了一个最大熵（MEM）图像重建程序，并精确测量了HXT准直器的x射线透过率函数（调制模式），这是MEM的关键参数。自1991年8月30日“Yohkoh”发射以来，我们将该程序应用于实际太阳耀斑数据，并对其进行了修订，使其适合于分析实际数据。1991年至1992年，我们在工作站建立了图像分析/处理系统，对太阳耀斑的硬x射线源进行了研究，并出版了“Yohkoh HXT数据手册第1期”。从这个项目可以证实：(1)HXT作为一个图像工作得很好，即，设计是正确的。(2) MEM程序提供的图像质量与预期的一样好。(3)发现太阳耀斑的x射线源在50 keV以上的高x射线能量时基本上是双重的。两个源的同时变化表明，电子在环的顶部附近被加速，它们沿着环沉淀到两个脚点，在那里它们发射x射线。(4)发现硬x射线源的高度随着x射线能量的增加而降低，这是支持上述解释的证据。

The aims of this project are to develop image reconstruction methods for hard X-ray imagery of the Fourier-synthesis type, especially for the Hard X-ray Telescope (HXT) onboard the SOLAR-A ("Yohkoh") satellite, and also to construct an image analysis system on a workstation. In 1990, we wrote a Maximum Entropy (MEM) image reconstruction program, and precisely measured the X-ray transmissivity functions (modulation patterns) of the HXT collimators which are key parameters of MEM. Since the launch of "Yohkoh" on 1991 August 30, we applied this program to actual solar flare data, and revised it to be suitable for analyzing actual data. In 1991 through 1992, we have constructed an image analysis/handling system on a workstation, conducted research on hard X-ray sources from solar flares, and published "The Yohkoh HXT Databook, No.1". From this project it is confirmed that:(1) The HXT works well as an imagery, i.e., the design is correct.(2) The MEM program provides images with as good image quality as expected.(3) X-ray sources of solar flares are found to be essentially double at high X-ray energies above 50 keV. Simultaneous variation of the two sources suggest that electrons are accelerated near the top of a loop and that they precipitate along the loop into the two footpoints where they emit X-rays.(4) The height of hard X-ray sources is found to decrease with increasing X-ray energies, which is supporting evidence for the above interpretation.