This image from Fermi's Large Area Telescope (LAT) shows how the entire sky looked on March 7 in the light of gamma rays with energies beyond 100 MeV. Although the Vela pulsar is the brightest continuous LAT source, it was outmatched this day by the X5.4 solar flare, which brightened the gamma-ray sun by 1,000 times. (Credit: NASA/DOE/Fermi LAT Collaboration)
Flares and other eruptive solar events produce gamma rays by accelerating charged particles, which then collide with matter in the sun's atmosphere and visible surface. For instance, interactions among protons result in short-lived subatomic particles called pions, which produce high-energy gamma rays when they decay. Nuclei excited by collisions with lower-energy ions give off characteristic gamma rays as they settle down. Accelerated electrons emit gamma rays as they collide with protons and atomic nuclei. Video : (Solar flares produce gamma rays by several processes, one of which is illustrated here. The energy released in a solar flare rapidly accelerates charged particles. When a high-energy proton strikes matter in the sun's atmosphere and visible surface, the result may be a short-lived particle -- a pion -- that emits gamma rays when it decays. )
Another Fermi instrument, the Gamma-ray Burst Monitor (GBM), observes the entire sky not blocked by the Earth at any given moment. Designed to detect light at energies from 8,000 eV to 40 MeV, the GBM's complementary capabilities give scientists access to a lower, but overlapping energy range where solar phenomena produce interesting features.
