Physics
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999spro.proc..353y&link_type=abstract
Solar Physics with Radio Observations, Proceedings of the Nobeyama Symposium, held in Kiyosato, Japan, Oct. 27-30, 1998, Edited
Physics
Scientific paper
Yohkoh observed two types of γ-ray flares on Nov.~6, 1997 and Aug.~18, 1998. The 1997 Nov.~6 flare showed strong narrow γ-ray lines superposed on the bremsstrahlung continuum, suggesting both protons and electrons were efficiently accelerated. A ratio of low-FIP (Mg, Si and Fe) to high-FIP (C, N, O and Ne) line fluxes wasenhanced by a factor of 3 in the decay phase of the flare compared to those in the rise and peak phases. A flux ratio of O to Ne lines and a fluence ratio of neutron capture to C lines indicated that the proton spectrum was essentially constant throughout the flare and its power law spectral index was 4.3±0.3. The photospheric 3He/Habundance ratio was estimated to be (1.5±0.5)×10-5 from the time profile of the neutron capture line at 2.22 MeV. It is consistent with that obtained from the 1991 June 4 flare. On the other hand, the 1998 Aug.~18 flare exhibited hard bremsstrahlung continuum without γ-ray lines, suggesting that electrons were preferentially accelerated to high energies (electron-dominated flare). The continuum spectrum varied with time. The power law spectral indices in the rise, peak and decay phases were 2.11, 1.85 and 2.25, respectively. Thecontinuum spectrum extended to 20 MeV but significantly steepened above 20 MeV, implying that electrons were not accelerated above a few tens of MeV.
Shiozawa A.
Suga Kazuharu
Yoshimori Masato
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