Energetic Gamma-Ray Emission from Solar Flares

Abstract

Recent advances in the γ -ray observations of solar flares by the Fermi satellite demand revisions in the hadronic γ -ray flux computation below 1 GeV. In this work, we utilize recently updated pion production cross sections, along with an accurate description of low-energy nuclear interactions. Applying these new interaction descriptions to model the Fermi Large Area Telescope solar flare data, we infer primary particle spectral parameters. Application of this new cross section description leads to significantly different spectral parameters compared to those obtained previously. Furthermore, the inclusion of nuclei in these calculations leads to a primary spectrum that is generally harder than that required from proton-only considerations. Finally, the flare data at lower MeV energies, detected by the Fermi Gamma-ray Burst Monitor, are shown to provide additional low-energy spectral information.