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 \cdot 10 ^ { 50 } erg , the initial hydrogen number density n ( 0 ) = 0.21 cm ^ { -3 } , the mean radius \overline { 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 .

Key words : supernova remnants , individual : IC 443 , X-rays , cosmic rays , \gamma -rays

PACS : 98.38.Mz , 98.70.Qy , 98.70.Rz , 98.70.Sa