We investigate the effect of the circumstellar medium density profile on the X-ray emission from outer ejecta knots in the Cassiopeia A supernova remnant using the 1 Ms Chandra observation .
The spectra of a number of radial series of ejecta knots at various positions around the remnant are analyzed using techniques similar to those devised in previous papers .
We can obtain a reasonable match to our data for a circumstellar density profile proportional to r ^ { -2 } as would arise from the steady dense wind of a red supergiant , but the agreement is improved if we introduce a small ( 0.2-0.3 pc ) central cavity around the progenitor into our models .
Such a profile might arise if the progenitor emitted a fast tenuous stellar wind for a short period immediately prior to explosion .
We review other lines of evidence supporting this conclusion .
The spectra also indicate the widespread presence of Fe-enriched plasma that was presumably formed by complete Si burning during the explosion , possibly via alpha-rich freezeout .
This component is typically associated with hotter and more highly ionized gas than the bulk of the O- and Si-rich ejecta .