Evidence for Recombining Plasma in the Supernova Remnant G346.6-0.2

Abstract

We present Suzaku results of the supernova remnant (SNR) G346.6-0.2. The X-ray emission has a center-filled morphology with a size of 67' × 8' within the radio shell. Neither an ionization equilibrium nor non-equilibrium (ionizing) plasma can reproduce the spectra remaining shoulder-like residuals in the 2-4 keV band. These structures are possibly due to a recombination of free electrons to the K-shell of He-like Si and S. The X-ray spectra were well-fitted with a plasma model in a recombination-dominant phase. We propose that the plasma was in a nearly full ionized state at a high temperature of ∼5 keV, and then the plasma changed to a recombining phase due to selective cooling of electrons to a lower temperature of ∼0.3 keV. G346.6-0.2 would be in an epoch of the recombining phase.