Iron-rich Ejecta in the Supernova Remnant DEM L71

Chandra X-ray observations of DEM L71, a supernova remnant (SNR) in the Large Magellanic Cloud (LMC), reveal a clear double-shock morphology consisting of an outer blast-wave shock surrounding a central bright region of reverse-shock-heated ejecta. The abundances of the outer shock are consistent with LMC values, while the ejecta region shows enhanced abundances of Si, Fe, and other species. However, oxygen is not enhanced in the ejecta; the Fe/O abundance ratio there is ≳5 times the solar ratio. Based on the relative positions of the blast-wave shock and the contact discontinuity in the context of SNR evolutionary models, we determine a total ejecta mass of ~1.5 M☉. Ejecta mass estimates based on emission measures derived from spectral fits are subject to considerable uncertainty because of the lack of knowledge of the true contribution of hydrogen continuum emission. Maximal mass estimates, i.e., assuming no hydrogen, result in 1.5 M☉ of Fe and 0.24 M☉ of Si. Under the assumption that an equal quantity of hydrogen has been mixed into the ejecta, we estimate 0.8 M☉ of Fe and 0.12 M☉ of Si. These characteristics support the view that in DEM L71, we see Fe-rich ejecta from a Type Ia supernova several thousand years after explosion.