Role of CME clusters and CME-CME interactions in producing sustained $\gamma$-ray emission

Atul Mohan, Pertti Makela, Natchimuthuk Gopalswamy +2

Fast (V${}_{\mathrm{CME}}$>1000$\mathrm{km}{\mathrm{s}}^{-1}$) coronal mass ejections (CMEs) capable of accelerating protons beyond 300MeV are thought to trigger hours-long sustained $\gamma$-ray emissi…