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

TL;DR

This study presents Suzaku X-ray observations of supernova remnant G346.6-0.2, revealing evidence of a recombining plasma phase characterized by spectral features indicative of electron recombination with He-like Si and S.

Contribution

It provides the first evidence of a recombining plasma in G346.6-0.2, demonstrating a transition from a high-temperature ionized state to a recombining phase.

Findings

Spectral residuals suggest recombining plasma rather than ionizing or equilibrium plasma.

The plasma was initially at 5 keV and cooled to 0.3 keV, leading to the recombining phase.

G346.6-0.2 is currently in a recombining plasma epoch.

Abstract

We present the Suzaku results of the supernova remnant (SNR) G346.6-0.2. The X-ray emission has a center-filled morphology with the size of 6' x 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 recombination of free electrons to the K-shell of He-like Si and S. The X-ray spectra are well fitted with a plasma model in a recombination dominant phase. We propose that the plasma was in nearly full ionized state at high temperature of 5 keV, then the plasma changed to a recombining phase due to selective cooling of electrons to lower temperature of 0.3 keV. G346.6-0.2 would be in an epoch of the recombining phase.