The Common Origin of High-energy Protons in Solar Energetic Particle Events and Sustained Gamma-ray Emission from the Sun

We report on the correlation between the number of >500 MeV protons (N_g) deduced from the Fermi/LAT >100 MeV sustained gamma-ray emission (SGRE) and the number of protons at 1 au (N_SEP) estimated from PAMELA mission’s solar energetic particle (SEP) measurements. The correlation is highly significant with a correlation coefficient of 0.77 and hence supports the shock origin of >300 MeV protons that interact with the solar chromosphere and resulting in pion decay observed as SGRE. The lack of correlation previously reported has been shown to be due to (i) a systematic underestimate of N_g in events originating close to the limb owing to the spatially-extended nature of SGRE, and (ii) a systematic underestimate of N_SEP in events originating at higher latitudes as a consequence of poor latitudinal connectivity. Correcting for these to effects, we find that the regression line is close to the N_g = N_SEP line. The close correlation found between N_SEP and N_g indicating their common origin (the CME-driven shock) is consistent with other significant correlations: (i) between the SGRE duration and the duration of the associated interplanetary type II radio burst, and (ii) between the SGRE fluence and CME speed.