ON THE EVOLUTION OF EJECTA FRAGMENTS IN COMPACT SUPERNOVA-REMNANTS

We examine the evolution of inhomogeneities (fragments) of supernova e jecta in compact supernova remnants by means of hydrodynamical modelli ng and simplified analytical calculations. Under the influence of inte nse post-shock cooling the fragments become strongly compressed as the y traverse the hot shocked region between the reverse and outer shocks of the remnants. We find that the most likely outcome of the interact ion of fragments with the reverse shock and the hot shocked region is their disruption, resulting in the generation of secondary fragments, Secondary fragments arriving at the thin and dense outer shell of the remnant give rise to brief X-ray flashes. Under suitable conditions th e primary fragments may traverse the hot shocked region without being completely destroyed, eventually reaching the outer shell as dense, el ongated structures. Collisions of such fragments with the shell are li kely to give rise to powerful X-ray flares.