Hα Polarization during a Well‐observed Solar Flare: Proton Energetics and Implications for Particle Acceleration Processes

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Abstract
Observations of polarization of chromospheric lines in solar flares can constrain the energy flux in accelerated protons. In this paper we analyze recently reported observations of Hα linear polarization obtained during a rather well observed flare on 1989 June 20. Modeling of the magnitude and orientation of the Hα polarization provides a constraint on the flux of low energy (200 keV) protons, while simultaneous gamma-ray and hard X-ray observations provide constraints on 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 both the absolute and relative roles of electrons and protons in the flare energy budget. We find that accelerated protons with energies 200 keV can contain a significant portion of the total energy released during the flare, consistent with a steep extrapolation of the proton spectrum to such relatively low energies. We discuss these results in light of a unified electron/proton stochastic particle acceleration model and show that the energetics are indeed consistent with this large proton energy content.