Observations and Interpretation of Behind the Limb Solar Flares Detected by Fermi-LAT and Other Instruments

The Fermi Large Area Telescope (LAT) is the most sensitive instrument ever deployed in space for observing > 30 MeV gamma-rays. During the past active period of the Sun the LAT has detected more than 40 flares up to GeV energies some of which occur behind the limb as determined by STEREO observations. We will present the observations on two such flares with significant flux of > 100 MeV (and some indication of 1 to 10 MeV detected by Fermi-GBM) gamma-rays coming from the visible disk while the flare and associated CMEs are initiated in active regions tens of degrees behind the visible limb of the Sun. We will consider acceleration of particles, their transport and radiative signatures, and the transfer of these radiation in the solar atmosphere to distinguish between (i) acceleration in the low corona, in a high corona trap, and/or in the CME driven shock; (ii) between continuous and prompt acceleration; and (iii) between electron bremsstrahlung and decay of pions produced by accelerated ions.