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   PR # 42094
   The soft X-ray emission seen shortly after a Type II supernova is the
   dominant radiative loss mechanism in SNR that are a few years old.
   The nature and evolution of this emission represents one of the major
   unexplored areas in the study of supernovae, but current telescopes
   make studies possible. To explain the emission, two theories have
   been proposed, a reverse shock model (with variations) and a cloud
   crushing model. Single X-ray spectra cannot distinguish between the
   two models, but the time evolution of the X-ray spectra should be a
   powerful diagnostic and here we propose to obtain the fundamental
   data that will constrain the models: high-quality X-ray spectra as a
   function of time for SN1986J, SN1978K (these will be second-epoch
   spectra), and SN 1993J.
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