HYDRODYNAMIC MODEL OF KEPLERS SUPERNOVA REMNANT CONSTRAINED BY EINSTEIN AND EXOSAT X-RAY-SPECTRA

We have used the EXOSAT spectrum of Kepler's supernova remnant (includ ing the Fe K line and the high-energy continuum) to further constrain its models. On the basis of the large abundances of Si, S and Fe requi red by a Sedov model, we have focused on models of young supernova rem nants in which the reverse shock (propagating into the stellar ejecta) is still active. We have built a relatively simple hydrodynamic code (assuming adiabatic expansion and ion-electron equilibrium) and couple d it to the ionization equations. The assumption of an SN II remnant w ith 5 M. ejecta dominated by hydrogen was tested. The simplest density structure (uniform ejecta and uniform ambient medium) fits the X-ray data fairly well when the ambient density and explosion energy are adj usted at 0.74 cm(-3) and 1 10(51) ergs, respectively. Small overabunda nces (2 to 3 times solar) of Si, S and Ar in the ejecta are enough to account for the observed line intensities. However the temperature is too low in the shocked ejecta to produce the Fe K line without exceedi ng the observed Fe L intensity. The shocked ambient medium is hot enou gh but a large overabundance of iron (4.6 times solar) is necessary. A s such an overabundance is hard to justify, we conclude that the model will have to be refined in order to get over this last stumbling bloc k. Other models were also tested: with M(ej) = 5 M. and ejecta of pure helium, with M(ej) = 1O M., and with Coulomb heated electrons. None i s able to produce the Fe K line in the ejecta.