Takaaki Tanaka, SLAC National Accelerator Laboratory
Galactic Cosmic Rays (GCRs) are widely believed to be accelerated at expanding shock waves of supernova remnants (SNRs) through the diffusive shock acceleration mechanism. It has been recognized that enhanced pion decay gamma-rays expected from SNRs that are interacting with molecular clouds could provide direct evidence of the nuclear component of GCRs accelerated at supernova shocks. We here report the first year observations with the Fermi LAT in the directions of such SNR-cloud systems. The extended GeV gamma-ray emission has been detected at least four SNRs. The observed gamma-rays can be explained reasonably by a combination of efficient acceleration of nuclear cosmic rays and shock-cloud interactions, shedding new light on the origin of GCRs.