EGRET OBSERVATIONS OF RADIO-BRIGHT SUPERNOVA-REMNANTS

The gamma-ray emission associated with radio-bright supernova remnants has been studied using data from the EGRET instrument aboard the Comp ton Gamma Ray Observatory. Five sources from The Second EGRET Catalog of High-Energy Gamma-Ray Sources are shown to be coincident with super nova remnants. The two strongest pointlike gamma-ray excesses which ar e coincident with supernova remnants are 2EG J2020+4026 with gamma Cyg and 2EG J0618+2234 with IC 443. The gamma-ray flux, E > 100 MeV, from the region of these two supernova remnants is (12.6 +/- 0.7) x 10(-7) photons cm(-2) s-1 and (5.0 +/- 0.4) x 10-7 photons cm(-2) s(-1), res pectively. The differential gamma-ray flux of both supernova remnants is consistent with a single power law, F proportional to E(-alpha), wi th alpha = 2.07 +/- 0.05 and 1.97 +/- 0.07 for gamma Cyg and IC 443, r espectively. A cosmic-ray origin model based on shock acceleration of cosmic rays is consistent with our results suggesting supernova remnan ts as an acceleration site, and possibly the origin, of Galactic cosmi c rays. Other mechanisms to explain the possible gamma-ray emission fr om supernova remnants are also discussed in the context of the EGRET o bservations.