Discovery of a Wind-Blown Bubble Associated with the Supernova Remnant G346.6-0.2: A Hint for the Origin of Recombining Plasma

Abstract

We report on CO and H I studies of the mixed-morphology supernova remnant (SNR) G346.6−0.2. We find a wind-blown bubble along the radio continuum shell with an expansion velocity of ∼ 10 km s −1 , which was likely formed by strong stellar winds from the high-mass progenitor of the SNR. The radial velocities of the CO/H I bubbles at V LSR = −82-−59 km s −1 are also consistent with those of shock-excited 1720 MHz OH masers. The molecular cloud in the northeastern shell shows a high-kinetic temperature of ∼ 60 K, suggesting that shock-heating occurred. The H I absorption studies imply that G346.6−0.2 is located on the far side of the Galactic center from us, and the kinematic distance of the SNR is derived to be 11.1 +0.5 −0.3 kpc. We find that the CO line intensity has no specific correlation with the electron temperature of recombining plasma, implying that the recombining plasma in G346.6−0.2 was likely produced by adiabatic cooling. With our estimates of the interstellar proton density 280 cm −3 and gamma-ray luminosity < 5.8 × 10 34 erg s −1 , the total energy of accelerated cosmic rays W p < 9.3 × 10 47 erg is obtained. A comparison of the age-W p relation to other SNRs suggests that most of the accelerated cosmic rays in G346.6−0.2 have been escaped from the SNR shell.