On the Origin of Long-duration Solar Gamma-ray Flares and Their Connection with SEPs

The mechanism producing long-duration solar gamma-ray events (LDGREs) is unresolved. Such events are characterized by high-energy (>100 MeV) pion-decay emission that can be detected for up to 10 hours after the flare impulsive phase. Candidate processes include: (1) prolonged acceleration/trapping of high-energy (> 300 MeV) protons in flare loops and (2) precipitation of energetic protons to the Sun's surface from the CME-driven coronal shock waves. LDGREs, or events with delayed/prolonged pion-dominated emission, have been detected by the SMM GRS, GRO EGRET, and Fermi LAT. To gain insight on their origin, we examine associated GOES X-ray bursts, LASCO CMEs, Wind Waves low-frequency radio bursts, and GOES high-energy proton events, and compare the properties of these various phenomena with the intensities and durations of the observed LDGREs.