Fermi detection of γ-ray emission from the M2 soft x-ray flare on 2010 June 12

The Geostationary Operational Environmental Satellite (GOES) M2-class solar flare, SOL2010-06-12T00:57, was modest in many respects yet exhibited remarkable acceleration of energetic particles. The flare produced an 50s impulsive burst of hard X- and γ-ray emission up to at least 400MeV observed by the Fermi Gamma-ray Burst Monitor and Large Area Telescope experiments. The remarkably similar hard X-ray and high-energy γ-ray time profiles suggest that most of the particles were accelerated to energies ≳300MeV with a delay of 10s from mildly relativistic electrons, but some reached these energies in as little as ∼ 3s. The γ-ray line fluence from this flare was about 10 times higher than that typically observed from this modest GOES class of X-ray flare. There is no evidence for time-extended >100MeV emission as has been found for other flares with high-energy γ-rays.