Suzaku Observations of the Supernova Remnant N23 in the Large Magellanic Cloud

Abstract

X-ray emission from the supernova remnant N23 in the Large Magellanic Cloud (LMC) has been studied using the X-ray Imaging Spectrometer (XIS) onboard Suzaku. Thanks to a superior energy resolution of the XIS in the soft X-ray band, we resolved H-like and He-like Oxygen K$\alpha$ emission lines from N23 with unprecedentedly high quality, and as a result, identified a new optically thin thermal emission component with a temperature of $\sim\ $0.2 keV, as well as that with a temperature of $\sim\ $0.5-0.7 keV, previously known. This alters the estimate of the ionization timescale, $n_{\rm e}t$, from $\sim\ $10$^{10-11}\ $cm$^{-3}\ $s to $\gtrsim\ $10$^{12}\ $cm$^{-3}\ $s. Under the assumption that N23 is still in the Sedov phase, its age, evaluated from the newly discovered low-temperature component, is $\sim\ $8000 yr, although it is possible that N23 has already moved into the radiative phase. The abundances of the heavy elements are found to be roughly consistent with those of the LMC average, which indicates that the origin of the X-ray emission of N23 is swept-up ambient material, as expected from its ionization timescale.