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A Statistical Study of Gamma-Ray Emitting Solar Flares Observed with Yohkoh

Yukari Matsumoto·Kazuo Makishima·Jun'ichi Kotoku·Masato Yoshimori·Kazuharu Suga·Takeo Kosugi·Satoshi Masuda·Kouji Morimoto
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Abstract

Gamma-ray emitting solar flares observed with Yohkoh were analyzed from a statistical viewpoint. The four-band hard X-ray (15--95 keV) photometric data, taken with the Hard X-ray Telescope onboard Yohkoh, were utilized in combination with the spectro-photometric gamma-ray (0.2--30 MeV) data obtained with the Gamma-Ray Spectrometer. The GOES class was also incorporated. Out of 2788 X-ray flares observed from 1991 October to 2001 December, 178 events with strong hard X-ray emission were selected. Among them, 40 flares were further found to show significant gamma-ray emission. A fractal dimension analysis and multi-band color--color plots of the 40 flares suggest that their soft X-ray to MeV gamma-ray spectral energy distributions involve at least four independent parameters. These are: (1) the overall flare size; (2) the relative intensities of the thermal vs. non-thermal signals; (3) the gamma-ray to hard X-ray intensity ratio; and (4) the hard X-ray spectral slope. These results are examined for possible selection effects. Also, the meanings of the third parameter are briefly considered.

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Yukari Matsumoto, Kazuo Makishima, Jun'ichi Kotoku, Masato Yoshimori, Kazuharu Suga, Takeo Kosugi, Satoshi Masuda, Kouji Morimoto. 2005-01-24. A Statistical Study of Gamma-Ray Emitting Solar Flares Observed with Yohkoh. https://doi.org/10.1093/pasj%2F57.1.211

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