Study of solar X-ray albedo by the upper earth atmosphere and fluorescent X-rays using the data obtained by the X-ray astronomy satellite

利用ASCA x射线卫星上的气体成像光谱仪（GIS）获得的数据，对太阳x射线的地球反照率及其长期变化进行了研究，得到了0.5 ~ 5kev能量范围内的x射线反照率光谱，其分辨率几乎可以探测到太阳活动整个周期内几种元素的k线。光谱可以用一个由三要素组成的模型来描述：(a) 2℃热发射，(b)通过地球大气反射对热发射的修正，以及(c)附加发射线。分量(a)是太阳日冕的平均辐射。太阳热x射线辐射的温度在数据统计范围内基本保持不变，两个分量的值分别为~ 300MK和500-1000MK，两个分量的强度随太阳活动周期的变化而变化，温度越高的分量振幅越大。较高的温度成分可能来自太阳耀斑的x射线发射，而较低的温度成分来自非耀斑的日冕。附加的发射谱线除了来自大气0和Ar的k谱线外，还包括Mg和Si的k谱线。Mg和Si谱线的能量比来自太阳热辐射主成分的谱线要低，强度要高。一种可能的解释是太阳日冕等离子体中的电离非平衡反射，ASTRO-EII将于2005年发射，预计将以更高的能量分辨率进行同样的研究。

We studied the earth albedo of the solar X-ray and its long term variation using die data obtained by the Gas Imaging Spectrometer (GIS) on board the X-ray satellite ASCA The X-ray albedo spectra in the energy range of 0.5-5keV were obtained with the resolution that enables detection of K-lines of several elements for almost the full span of solar activity. The spectra can be described with a model that consists of three elements : (a) 2-temperature thermal emission, (b) modification of the thermal emission through the reflection by the earth atmosphere, and (c) additional emission lines. The component (a) is the averaged emission from the solar coronae. The temperatures of the thermal X-ray emission from the sun stayed almost constant within the statistics of the data, and the values of the two components are 〜300MK and 500-1000MK respectively The intensities of the two components showed variation in accordance with the solar activity cycle, of which amplitude was larger for the higher temperature component. The higher temperature component is probably from the X-ray emission of the solar flares, and the lower temperature component is from the non-flaring coronae. The additional emission lines include K-lines of Mg and Si aside from the K-lines from the atmospheric 0 and Ar. The Mg and Si lines have lower energies and higher intensities than those expected from the main component of the thermal emission from the sun. One of the possible explanations is the ionization non-equilibrium eflect in the solar coronal plasma ASTRO-EII that is to be launched in 2005 is expected to enable same line of research with superior energy resolution.