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 non-solar elemental abundance ratios. In each case, Si and S are unequivocally overabundant compared to solar based purely on the measured equivalent width of the K$\alpha$ line complex. Detailed nonequilibrium ionization spectral analysis of these remnants, using a single temperature, single ionization age model, confirm the overabundances, yielding Si, S and Ar abundances many times their solar values: 3 to 5 times solar for G337.2-0.7 and greater than 3 to 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 as well are relatively underabundant. This is the first detection of metal-rich, non-solar 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 $4 \pm 2$ kpc for G309.2-0.6). From the implied sizes of the remnants at these distances we infer relatively young ages (2000 to 4500 years for G337.2-0.7, and 700 to 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.