Discovery of molecular and atomic clouds associated with the gamma-ray supernova remnant Kesteven 79

TL;DR

This study used CO observations to identify molecular and atomic clouds interacting with the gamma-ray supernova remnant Kesteven 79, revealing details about its environment, distance, and potential cosmic-ray origin.

Contribution

First detailed CO and atomic gas analysis of Kesteven 79 linking gas interactions with gamma-ray emission and shock heating effects.

Findings

Molecular and atomic gases interact with the SNR at ~80 km/s

SNR is at a distance of ~5.5 kpc with a radius of ~8 pc

Estimated cosmic-ray proton energy is ~5 x 10^{48} erg

Abstract

We carried out $^{12}$CO($J$ = 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 $\sim20$ arcsec. We identified molecular and atomic gas interacting with Kesteven 79 whose radial velocity is $\sim80$ 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 $\sim4$ 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 $\sim24$ K, owing to heating by the supernova shock. We determined the kinematic distance to the SNR to be $\sim5.5$ kpc and the radius of the SNR to be $\sim8$ pc. The average interstellar proton density inside of the SNR is $\sim360$ cm$^{-3}$, of which atomic protons comprise only $\sim10$ $\%$. Assuming a hadronic origin for the gamma-ray emission, the total cosmic-ray proton energy above 1 GeV is estimated to be $\sim5 \times 10^{48}$ erg.