Evidence for Enhanced Accelerated 3He in Solar Flares from Gamma-Ray Spectroscopy
Abstract
The 3He abundance in impulsive solar energetic particle (SEP) events is enhanced up to several orders of magnitude compared to its photospheric value of 3He/4He = 1 - 3 X 10^-4. Interplanetary magnetic field and timing observations suggest these events are related to solar flares. Observations of 3He in flare-accelerated ions would clarify the relationship between these two phenomena. Energetic 3He interactions in the solar atmosphere produce gamma-ray nuclear-deexcitation lines, both lines that are also produced by protons and alpha particles and lines that are essentially unique to 3He. Gamma-ray spectroscopy can therefore reveal enhanced levels of accelerated 3He. Here we identify all significant deexcitation lines produced by 3He interactions in the solar atmosphere and evaluate their production cross sections. We find that enhanced 3He can affect the entire spectrum. We identify gamma-ray line features whose yield ratios depend dramatically on the 3He abundance. We determine the accelerated 3He/alpha ratio by comparing these ratios with flux ratios measured previously from the gamma-ray spectrum obtained by summing the 19 strongest flares observed with the Solar Maximum Mission Gamma-Ray Spectrometer. All six flux ratios investigated show enhanced 3He, confirming earlier suggestions. The 3He/alpha weighted mean of these new measurements ranges from 0.05 to 0.3 (depending on the assumed accelerated alpha/proton ratio) and has a <1 X 10^-3 probability of being consistent with the photospheric value.
- Publication:
-
Solar Heliospheric and INterplanetary Environment (SHINE 2017)
- Pub Date:
- July 2017
- Bibcode:
- 2017shin.confE..83M