Shocked molecular gas associated with the supernova remnant W28

We report on mapping observations of the CO J = 3-2 and CO J = 1-0 lines to ward supernova remnant (SNR) W28, which is supposed to be an EGRET gamma-ra y source. A broad CO line emission (maximum linewidth reaches 70 km s(-1)), which suggests an interaction between the molecular cloud and W28 SNR, was detected. Moreover, the distribution of the unshocked and shocked gas is c learly resolved. The distribution of the shocked gas is similar to that of the radio-continuum emission, and tends to be stronger along the radio-cont inuum ridge. The unshocked gas is displaced by 0.4-1.0 pc outward with resp ect to the shocked gas. The spatial relationship between shocked and unshoc ked gas has been clarified for the first time for the SNR-cloud interaction . All of the known OH maser spots are located along the filament of the sho cked gas. These facts convincingly indicate that W28 SNR interacts with the molecular cloud.