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U. Hwang (NASA GSFC, UMD), R. Petre (NASA GSFC), J. P. Hughes (Rutgers University)
The supernova remnant W49B has one of the most impressive line spectra obtained by the ASCA X-ray Observatory. Based on line intensity ratios, Fujimoto et al. (1995) have suggested that the elements Si, S, Ar, and Ca have different ionization ages and/or temperatures. We show that when the line centroids are also considered, the Si emission requires more than one spectral component. A simple model with two such components is shown to satisfactorily reproduce the entire ASCA spectrum between energies of 0.6 to 10 keV. The hotter component is in collisional ionization equilibrium and is from ejecta, based on its highly enhanced element abundances; the cooler component is less ionized and its abundances are less well-constrained, but it may also arise from ejecta. The X-ray spectrum shows a weak line feature near 5.7 keV that may be emission from Cr, an element not previously detected in X-ray spectra of cosmic sources. As most supernova remnants are expected to remain in ionization nonequilibrium for most of their X-ray lifetime, it is unusual to find an ejecta-dominated remnant near ionization equilibrium. This suggests that W49B is in an unusually dense environment.
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