Top: bolometric light curve for the 1D CMFGEN models 1D-X1 and 1D-X2b. Bottom: Mass density, initial ⁵⁶Ni mass fraction, electron density, gas temperature, and hydrogen ionization fraction vs. velocity for models 1D-X1 (solid) and 1D-X2b (dashed) at 44 d after explosion. These two models vary in the outer ejecta structure, the inner core structure, and the ⁵⁶Ni mixing adopted (strong or weak, presence or absence of a ⁵⁶Ni-rich shell at a Lagrangian mass of 12 M_⊙, corresponding to a velocity of about 4000 km s⁻¹ in the resultingejecta). The two models have the same mass-density profile outside of the inner ejecta (with the exception of the regions beyond 10 000 km s⁻¹), but different electron-density profiles because of the different ⁵⁶Ni profiles.