Hα polarization during a well-observed solar flare:: Proton energetics and implications for particle acceleration processes

Observations of polarization of chromospheric lines in solar hares can constrain the energy flux in accelerated protons. In this paper we analyze recently reported observations of H alpha linear polarization obtained during a rather well observed hare on 1989 June 20. Modeling of the magnitude and orientation of the H alpha polarization provides a constraint on the flux of low energy (greater than or similar to 200 keV) protons, while simultaneous gamma-ray and hard X-ray observations provide constraints on the fluxes of greater than or similar to 10 MeV protons and greater than or similar to 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 greater than or similar to 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.