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OSSE ABSTRACT

Gamma-Ray Line Observations of the 2000 July 14 Flare and SEP Impact on the Earth


G.H. Share, R.J. Murphy, A.J. Tylka, R.A. Schwartz, M. Yoshimori, K. Suga, S. Nakayama, H. Takeda

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Abstract. The HXS and GRS detectors on Yohkoh observed the 2000 July 14, X5.7 flare, beginning at ~10:20 UT, ~4 m before the peak in soft X rays. The hard X rays and gamma rays peaked ~3 m later at ~10:27 UT. Solar gamma-ray emission lasted until ~10:40 UT. Impact of high-energy ions at the Sun is revealed by the gamma-ray lines from neutron capture, annihilation radiation and de-excitation that are visible above the bremsstrahlung continuum. From measurement of these lines we find that the flare-averaged spectrum of accelerated protons is consistent with a power law >10 MeV with index 3.14 0.15 and flux 1.1 X 10^32 MeV^-1 at 10 MeV. We estimate that there were ~1.5 X 10^30 erg in accelerated ions if the power law extended without a break down to 1 MeV; this is about 1% of the energy in electrons >20 keV from measurements of the hard X rays. We find no evidence for spectral hardening in the hard X rays that has been suggested as a predictor for the occurrence of solar energetic particle (SEP) events. This was the third largest proton event above 10 MeV since 1976. The GRS and HXS also observed gamma-ray lines and continuum produced by the impact of SEP on the Earth's atmosphere beginning about 13 UT on July 14. These measurements show that the SEP spectrum softened considerably over the next 24 hours. We compare these measurements with proton measurements in space.