CO J=1-0 AND J=2-1 LINE OBSERVATIONS OF THE MOLECULAR-CLOUD-BLOCKED SUPERNOVA REMNANT 3C434.1

We present the results of CO emission line observations toward the semicircular Galactic supernova remnant (SNR) 3C434.1 (G94.0+1.0). We mapped an area covering the whole SNR in the (CO)-C-12 J = 1-0 emission line using the Seoul Radio Astronomy Observatory 6 m telescope and found a large molecular cloud superposed on the faint western part of the SNR. The cloud was elongated along the north-south direction and showed a very good spatial correlation with the radio features of the SNR. We carried out (CO)-C-12 J = 2-1 line observations of this cloud using the Kolner Observatorium fur Sub-Millimeter Astronomie 3 m telescope and found a region in which the (CO)-C-12 J = 2-1 to J = 1-0 ratio was high (similar to 1.6). This higher excitation, together with the morphological relation, strongly suggested that the molecular cloud was interacting with the SNR. The systemic velocity of the molecular cloud (-13 km s(-1)) gave a kinematic distance of 3.0 kpc to the SNR-molecular cloud system. We derived the physical parameters of the SNR based on this new distance. We examined the variation of the radio spectral index over the remnant and found that it was flatter in the western part, wherein the SNR was interacting with the molecular cloud. We therefore propose that 3C434.1 is the remnant of a supernova explosion that occurred just outside the boundary of a relatively thin, sheet-like molecular cloud. We present a hydrodynamic model showing that its asymmetric radio morphology can result from its interaction with this blocking molecular cloud.