Where was the Iron Synthesized in Cassiopeia A?

Abstract

We investigate the properties of Fe-rich knots on the east limb of the Cassiopeia A supernova remnant using observations with Chandra/ACIS and analysis methods developed in a companion paper. We use the fitted ionization age and electron temperature of the knots to constrain the ejecta density profile and the Lagrangian mass coordinates of the knots. Fe-rich knots which also have strong emission from Si, S, Ar, and Ca are clustered around mass coordinates q~0.35-0.4 in the shocked ejecta; for ejecta mass 2M_sun, this places the knots 0.7-0.8 M_sun out from the center (or 2-2.1 M_sun, allowing for a 1.3 M_sun compact object). We also find an Fe clump that is evidently devoid of line emission from lower mass elements, as would be expected if it were the product of alpha-rich freeze out; the mass coordinate of this clump is similar to those of the other Fe knots.