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

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 rays peaked 3 m later at 10:27 UT. Solar -ray emission lasted until 10:40 UT. Impact of high-energy ions at the Sun is revealed by the -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 flareaveraged spectrum of accelerated protons is consistent with a power law 10 MeV with index 3.14 0.15 and flux 1.1 10(expn 32) MeV 1 at 10 MeV. We estimate that there were 1.5 10(expn 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 -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.
2001, Solar Physics, 204: p. 43. Prepared in collaboration with the Hughes/STX Corp, NASA Goddard Space Flight Center, Greenbelt, MD, and the Department of Physics, Rikkyo University, Tokyo, Japan.