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

TL;DR

This study investigates the supernova remnant G346.6-0.2, revealing a wind-blown bubble likely formed by stellar winds, and explores the origin of its recombining plasma, cosmic ray acceleration, and shock interactions through multi-wavelength observations.

Contribution

The paper provides the first detailed analysis linking wind-blown bubbles and shock-heated molecular clouds to the origin of recombining plasma in G346.6-0.2, with new estimates of cosmic ray energy and remnant distance.

Findings

Identification of a wind-blown bubble with ~10 km/s expansion velocity.

Recombining plasma likely produced by adiabatic cooling, not correlation with molecular cloud temperature.

Most cosmic rays have escaped from the SNR shell, with an estimated total energy of <9.3×10^{47} erg.

Abstract

We report on CO and HI 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 $\sim10$ 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/HI bubbles at $V_\mathrm{LSR} = -82$-$-59$ 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 $\sim60$ K, suggesting that shock-heating occurred. The HI 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 $11.1_{-0.3}^{+0.5}$ 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 $< 5.8 \times 10^{34}$ erg s$^{-1}$, the total energy of accelerated cosmic rays $W_{\rm p} < 9.3 \times 10^{47}$ erg is obtained. A comparison of the age-$W_{\rm p}$ relation to other SNRs suggests that most of the accelerated cosmic rays in G346.6$-$0.2 have been escaped from the SNR shell.