Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apjs...90..639y&link_type=abstract
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 90, no. 2, p. 639-643
Astronomy and Astrophysics
Astronomy
16
Gamma Ray Astronomy, Particle Acceleration, Positron Annihilation, Solar Flares, Angular Distribution, Bessel Functions, Bremsstrahlung, Gamma Ray Spectrometers, Line Spectra
Scientific paper
We present gamma-ray observations of the 1991 October 27, November 15, and December 3 flares with the Yohkoh gamma-ray and hard X-ray spectrometers. The October 27 flare (X6.1/3B) shows significant gamma-ray line emission, and the temporal evolution of the gamma-ray line-to-bremsstrahlung flux ratio indicates that protons and electrons were complicatedly accelerated during flare. The December 3 flare (X2.0/2B) shows a strong bremsstrahlung continuum extending to 10 MeV and indicates that electrons were preferentially accelerated to 10 MeV. A line feature at 420 keV was observed from the November 15 flare (X1.0/3B). This is most likely due to a compound of redshifted nuclear deexcitation lines of Be (429 keV) and Li(478 keV) resulting from He-He reactions. The spectral feature indicates that the accelerated He nuclei suffer strong pitch-angle scattering in the corona and form a downward-peaked distribution. Furthermore, the November 15 flare exhibits evidence of positron annihilation line at 511 keV. The positron production processes and the electron density of the annihilation region are discussed on the basis of the temporal characteristics of 511 keV line emission.
Hiraoka Takuji
Kawabata Kiyoshi
Morimoto Kanji
Ohki Kenichiro
Sato Joe
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