Magnetic Flux Reconnection in Flaring Active Regions with Sustained Gamma-Ray Emission

Abstract

Abstract Characteristics of sustained >100 MeV γ-ray emission (SGRE) events observed by the Large Area Telescope on Fermi were recently reported by Share et al. Their spectra are consistent with the decay of pions produced by >300 MeV protons and appear spectrally and spatially distinct from preceding associated flares. The source(s) of the sustained production of the >300 MeV protons is uncertain, but acceleration in coronal/interplanetary shock waves driven by coronal mass ejections, followed by a return of the protons back to the Sun, is favored. This scenario requires proton transport through converging magnetic fields behind the shock, which might result in considerable reflection of the protons back into space, and 1 au observations of the associated solar energetic proton (SEP) events do not always include a population of E > 300 MeV protons. Alternative source candidates that involve trapping or continued acceleration of SEPs in coronal loops have been considered. The energy release rates from magnetic reconnection in flaring active regions (ARs) have been measured with a new technique, and in this work we compare those measured flux reconnection rates with emission profiles in 11 SGRE events. In general, the magnetic reconnection event is nearly or completely finished before the bulk of the γ-ray emission, which argues against scenarios of continued proton acceleration in the flaring ARs.