ASCA Observations of the Twin Supernova Remnants in the Large Magellanic Cloud, DEM L316

We report results from an ASCA X-ray study of DEM L316, an emission nebula in the Large Magellanic Cloud (LMC) consisting of two closely-spaced supernova remnants (SNRs). The SIS image shows separate X-ray sources located at the positions of the two radio- and optically-emitting SNR shells, 0547--69.7A and 0547--69.7B (hereafter, shell A and shell B). The individual X-ray spectrum of each shell is well described by optically-thin thermal emission, although the characteristics of the emission differ in important details between them. Shell A exhibits strong iron L emission, which we attribute to the presence of iron-rich ejecta, leading to the suggestion that this SNR originates from a type Ia SN, an explosion of a moderate mass progenitor. Shell B, on the other hand, has a chemical composition similar to that of the interstellar medium of the LMC, and so its X-ray emission is dominated by swept-up matter. The different spectral features strongly disfavor the hypothesis that the two shells are due to one supernova explosion into an interconnected bubble. We could not obtain evidence which positively supports the collision between two SNRs.