Hydrodynamic model of Kepler's supernova remnant constrained by EINSTEIN and EXOSAT X-ray spectra.

We have used the EXOSAT spectrum of Kepler's supernova remnant (including 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 required by a Sedov model, we have focused on models of young supernova remnants 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 coupled it to the ionization equations. The assumption of an SN II remnant with 5M_sun_ 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 adjusted at 0.74cm^-3^ and 1x10^51^ergs, respectively. Small overabundances (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 exceeding the observed Fe L intensity. The shocked ambient medium is hot enough but a large overabundance of iron (4.6 times solar) is necessary. As 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 block. Other models were also tested: with M_ej_=5M_sun_ and ejecta of pure helium, with M_ej_=10M_sun_, and with Coulomb heated electrons. None is able to produce the Fe K line in the ejecta.