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The X-Ray Iron Emission from Tycho's Supernova Remnant

We present the results of broadband spectral model fits to the X-ray spectrum of Tycho's supernova remnant obtained by the Solid-State Imaging Spectrometers on the ASCA Observatory. We use single temperature, single ionization age, nonequilibrium ionization models to characterize the ejecta and the blast-shocked interstellar medium. Previous spectral studies have suggested that the Fe ejecta in this Type Ia remnant are stratified interior to the other ejecta. These studies, however, have generally restricted their attention to the Fe K blend at 6.5 keV. ASCA provides data over a broad energy range that allow the placement of important constraints simultaneously from the Fe L emission near 1 keV, as well as the Fe K emission. We find that the simplest models, with emission from the ejecta and blast wave each at a single temperature and ionization age, severely underestimate the flux in the Fe K blend. These models also show that there is little Fe emission associated with the Si and S ejecta shell, which has an average temperature kT ~ 0.86 keV and ionization age net ~ 1011 cm-3 s. The blast-shocked interstellar medium has abundances roughly 0.3 times the solar value, while the ejecta—with the exception of Fe—have relative abundances that are typical of Type Ia supernovae. The addition of another component of Fe emission—which we associate with ejecta—at a temperature at least 2 times higher and an ionization age ~100 times lower than the Si ejecta does provide a good fit to the spectrum. This model is consistent with imaging results. Although fluorescent emission from dust in the remnant may contribute to the Fe K flux, we conclude that it is unlikely to be the dominant component.