X-Ray Line Emission from Supernova Remnants and Models for Nonequilibrium Ionization

Abstract

An extensive grid of nonequilibrium ionization models for the X-ray spectra of adiabatic supernova remnants (SNRs) is described. The models are compared to the SSS spectra of remnants in the LMC, the Tycho SNR, and SNR 1006. In Tycho, we show that the observed spectrum requires significantly enhanced abundances of Si and S, and that this conclusion is independent of the detailed ionization and thermal structure in the remnant. We find that the SSS spectrum of SNR 1006 can be fit reasonably by a thermal emission model with abundances of about one half solar. In this model, the weak line emission results from the very low ionization state in the remnant, and not because the X-ray emission is non-thermal. We argue that the failure to detect strong Fe line emission in young Type I SNRs poses a severe problem for models of Type I SN, which predict that most of the ejecta be iron. Finally, the results of UV observations of a star behind SNR 1006 are mentioned; these observations show that the remnant contains a large amount of rapidly moving, cold iron.