Discovery of Molecular and Atomic Clouds Associated with the Gamma-Ray Supernova Remnant Kesteven 79

We carried out ¹²CO(J = 1-0) observations of the Galactic gamma-ray supernova remnant (SNR) Kesteven 79 using the Nobeyama Radio Observatory 45 m radio telescope, which has an angular resolution of ∼20 arcsec. We identified molecular and atomic gas interacting with Kesteven 79, whose radial velocity is ∼80 km s^-1. The interacting molecular and atomic gases show good spatial correspondence with the X-ray and radio shells, which have an expanding motion with an expanding velocity of ∼4 km s^-1. The molecular gas associated with the radio and X-ray peaks also exhibits a high intensity ratio of CO 3-2/1-0 > 0.8, suggesting a kinematic temperature of ∼24 K, owing to heating by the supernova shock. We determined the kinematic distance to the SNR to be ∼5.5 kpc and the radius of the SNR to be ∼8 pc. The average interstellar proton density inside of the SNR is ∼360 cm^-3, of which atomic protons comprise only ∼10%. Assuming a hadronic origin for the gamma-ray emission, the total cosmic-ray proton energy above 1 GeV is estimated to be ∼5 × 10⁴⁸ erg.