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A.G. Emslie, J.A. Miller (UAH), E. Vogt, J.-C. Hénoux, S. Sahal-Bréchot (Meudon)
Observations of polarization of chromospheric lines in solar flares can constrain the proton energy flux during the flare. In this paper, we analyze recently-reported observations of H\alpha linear polarization obtained during a rather well-observed flare on 1989 June~20. Modeling of the magnitude and orientation of the H\alpha polarization provides a constraint on the flux of low energy (~0.2~MeV) protons, while simultaneous gamma-ray and hard X-ray observations provide the fluxes of ~10~MeV protons, and ~50~keV electrons, respectively. These, plus information on the energetics of the low-temperature and high-temperature thermal emissions, permit evaluation of the relative role of electrons and protons in exciting the flare plasma. We find that above about 200~keV, accelerated protons significantly dominate the flare energy budget, overwhelming electrons by at least two orders of magnitude. We discuss these results in light of a unified electron/proton stochastic particle acceleration model, and show that the energetics are indeed consistent with the broad range of observational data.
This work was supported by NASA's Office of Space Science and by an NSF/CNRS International Collaboration Award.