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 toward supernova remnant (SNR) W28, which is supposed to be an EGRET gamma-ray 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 clearly resolved. The distribution of the shocked gas is similar to that of the radio-continuum emission, and tends to be stronger along the radio-continuum ridge. The unshocked gas is displaced by 0.4-1.0 pc outward with respect to the shocked gas. The spatial relationship between shocked and unshocked 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 shocked gas. These facts convincingly indicate that W28 SNR interacts with the molecular cloud.