The Total Spectrum of Solar X-rays and Its Long-Term Variation Obtained from Earth Albedo Data of ASCA GIS
Abstract
We report on the spectrum of solar X-rays and its long-term variation obtained from Earth albedo data of ASCA/GIS. GIS is a set of gas scintillation counters which cover the energy range of 0.5--10 keV. We accumulated GIS data of the Earth albedo for the period of 1993--2000 and analyzed spectra for each year. The period spans from the declining phase of solar cycle 22 to the rising phase of cycle 23. Although the spectral resolution of the GIS is moderate, the analyzed data are unique because of the long time coverage and relatively wide energy range in the X-ray band. The spectra were fit with a model that consists of solar X-rays reflected by neutral matter, and fluorescent lines from the Earth's atmosphere. Major results on the solar X-rays can be summarized as follows. (1) The solar X-ray spectra obtained by ASCA/GIS can be described with a two-temperature (∼0.3 keV and ∼0.5--1 keV) thermal emission from an optically-thin plasma. The higher-temperature component is interpreted to be mostly from flares, and the dominant lower-temperature component is from the non-flaring corona. (2) The intensity of the two components showed a variation in accordance with the solar activity cycle. The amplitude of the variation was a factor of 13 in the 0.5--2 keV band, where the lower-temperature component is dominant, and a factor of 30 in the 3--5 keV band, where the higher-temperature component is dominant. (3) Significant variation was not detected in the year-averaged temperatures of the two components during the observation period. Results on the fluorescent lines of Earth-origin will be reported elsewhere.
- Publication:
-
8th Asian-Pacific Regional Meeting, Volume II
- Pub Date:
- 2002
- Bibcode:
- 2002aprm.conf..435I