Providing the first evidence of a sub-MCh progenitor for the Type Ia SNR DEM L71

We propose a deep observation of DEM L71, a middleaged Type Ia SNR in the LMC,primarily using the Reflection Grating Spectrometers (RGS). Previous XMMNewtonand Chandra studies of this SNR revealed the centrallypeaked emission from theFerich ejecta, indicating that the whole supernova ejecta have been heated bythe reverse shock. Our analysis of the existing RGS data indicates an unusuallylow Ni/Fe mass ratio, although its uncertainties are somewhat large.Theoretically, such low Ni/Fe ratio is expected only for a thermonuclearexplosion of a subChandrasekharmass white dwarf (subMCh WD). With thisproposed observation, we will put a stringent constraint on the Ni/Fe ratio,providing the first robust evidence of the subMCh progenitor for a single Type Ia SN/SNR. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]