Two New Ejecta-dominated Galactic Supernova Remnants: G337.2–0.7 and G309.2–0.6

We present the analysis of new X-ray observations of two Galactic radio supernova remnants (SNRs), G337.2-0.7 and G309.2-0.6. Both remnants exhibit line-rich thermal spectra that require highly nonsolar elemental abundance ratios. In each case, Si and S are unequivocally overabundant compared to solar, based purely on the measured equivalent width of the Kα line complex. Detailed nonequilibrium ionization spectral analysis of these remnants, using a single-temperature, single ionization age model, confirms the overabundances, yielding Si, S, and Ar abundances many times their solar values: 3-5 times solar for G337.2-0.7 and greater than 3-10 times solar for G309.2-0.6. We also find that for both remnants, Ne and Mg are underabundant relative to Si, and for G309.2-0.6, Ca and Fe are relatively underabundant as well. This is the first detection of metal-rich, nonsolar abundance material in these remnants, identifying them as young ejecta-dominated SNRs. Further support for their youth comes from the distances that we estimate from the fitted column densities (less than 15 kpc for G337.2-0.7, and 4 ± 2 kpc for G309.2-0.6). From the implied sizes of the remnants at these distances we infer relatively young ages (2000-4500 years for G337.2-0.7 and 700-4000 years for G309.2-0.6). Finally, we note that no compact object has yet been found within G337.2-0.7, but an X-ray point source is evident within the radio shell of G309.2-0.6, although its nature remains unknown.