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

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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.