  We examine the hypothesis that some supernova remnants (SNRs) may be
responsible for some unidentified gamma-ray sources detected by EGRET
instrument aboard the Compton Gamma Ray Observatory. If this is the case,
gamma-rays are produced via pion production and decay from direct inelastic
collisions of accelerated by SNR shock wave ultrarelativistic protons with
target protons of the interstellar medium. We develop a 3-D hydrodynamical
model of SNR IC 443 as a possible cosmic gamma-ray source 2EG J0618+2234. The
derived parameters of IC 443: the explosion energy E_o=2.7*10^{50} erg, the
initial hydrogen number density n(0)=0.21 cm^{-3}, the mean radius R=9.6 pc and
the age t=4500 yr result in too low gamma-ray flux, mainly because of the low
explosion energy. Therefore, we investigate in detail the hydrodynamics of IC
443 interaction with a nearby massive molecular cloud and show that the reverse
shock wave considerably increases the cosmic ray density in the interaction
region. Meantime, the Rayleigh-Taylor instability of contact discontinuity
between the SNR and the cloud provides an effective mixing of the containing
cosmic ray plasma and the cloud material. We show that the resulting gamma-ray
flux is consistent with the observational data.
