Measured photon fluxes as a function of energy from the flare of 12 June 2010 together with an approximate fit including the GEANT4 simulated spectrum of Fig. 6, a single power-law photo spectrum, and a power-law spectrum with exponential turnover at high energy. The parameters of the various components are shown in the bottom left corner. The fitting procedure is detailed in the text. The vertical dashed lines near 30 MeV show the precise boundaries of the energy ranges of GBM (< 30 MeV) and LAT (> 30 MeV).