Cavity of Molecular Gas Associated with Supernova Remnant 3C 397

Understand

3C 397 is a radio and X-ray bright Galactic supernova remnant (SNR) with an unusual rectangular morphology.

• Our CO observation obtained with the Purple Mountain Observatory at Delingha reveals that the remnant is well confined in a cavity of molecular gas, and embedded at the edge of a molecular cloud (MC) at the local standard of rest systemic velocity of ~32 km/s.
• The cloud has a column density gradient increasing from southeast to northwest, perpendicular to the Galactic plane, in agreement with the elongation direction of the remnant.
• This systemic velocity places the cloud and SNR 3C 397 at a kinematic distance of ~10.3 kpc.