Other
Scientific paper
May 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.4107b&link_type=abstract
American Astronomical Society, 180th AAS Meeting, #41.07; Bulletin of the American Astronomical Society, Vol. 24, p.795
Other
Scientific paper
The hard X-ray spectrometer on the International Cometary Explorer (ICE -- formerly known as ISEE-3) spacecraft consisted of a NaI (Tl) scintillator, 22 cm(2) in area and surrounded by a plastic anticoincidence shield. The instrument measured photon spectra in 12 channels with a nominal energy range of 26 keV to 3.2 MeV. The exact X-ray energy range could be varied by command. Typically, the time resolution was 0.5 -- 4.0 seconds depending on the energy channel, with a complete spectrum being read out every 4 seconds. Of the solar flares observed by the hard X-ray spectrometer during the period August 1978 -- December 1986, we found approximately 7000 solar flares for which power law photon spectra covering at least two energy channels could be fit to both the observed peak counting rates and the total photon counts. The effective sensitivity of this data base is approximately 1.6 photons/cm(2) sec for photons with energy >30 keV. This data base was used to determine the number of hard X-ray flares observed per day above various thresholds of photon energy. The observed occurrence frequencies were corrected for data gaps and binned by month. In addition to the occurrence frequency of hard X-ray flares, variation of average spectral parameters during the solar cycle was also examined. The slope of the size distribution of hard X-ray flares is found to vary substantially during the solar cycle with pronounced changes especially during the 155-day recurrence periods. The size distribution tends to be significantly flatter in the maximum phase of the 155-day periods than in the minimum phase. This is consistent with results found in a study of SMM-HXRBS results by Bai (1992). A comparison of the long term variations of the hard X-ray flares with other related solar activity parameters, such as Hα flares and soft X-ray flares, will be presented. Implications of these results with regard to the mechanisms of the solar cycle variation will be discussed.
Asztalos B. B.
Bromund Kenneth R.
Kane Sharad R.
Loran Jon M.
McTiernan James M.
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