CSM density profile as a function of the SN shell expansion radius. The solid line gives the best‐fit CSM density profile of ﹩\rho _{\mathrm{csm}\,}\propto r^{-1.9}﹩ for the ROSAT (open squares) and Chandra (filled squares) measurements of SN 1994I. The CSM density profile with ﹩\rho _{\mathrm{csm}\,}\propto r^{-1.6}﹩ based on ROSAT observations of SN 1993J is drawn for comparison (dashed line and open triangles; Immler et al. 2001).