N49: THE FIRST ROBUST DISCOVERY OF RECOMBINING PLASMA IN AN EXTRA GALACTIC SUPERNOVA REMNANT

Abstract

Recent discoveries of recombining plasmas (RPs) in supernova remnants (SNRs) have dramatically changed our understanding of SNR evolution. To date, a dozen RP SNRs have been identified in the Galaxy. Here, we present Suzaku deep observations of four SNRs in the LMC, namely, N49, N49B, N23, and DEM L71, for accurate determination of their plasma states. Our uniform analysis reveals that of these SNRs, only N49 is in the recombining state, which is the first robust discovery of an RP from an extra-galactic SNR. Given that RPs have only been identified in core-collapse SNRs, our results strongly suggest a massive star origin for this SNR. On the other hand, no clear evidence of an RP is confirmed in N23, for which detection of recombination lines and continua was previously claimed. Comparing the physical properties of the RP SNRs identified so far, we find that all of them can be categorized into the "mixed-morphology" class, interacting with surrounding molecular clouds. This might be a key to determining the formation mechanisms of RPs.