Spectral evolution of the gamma-ray emission from the delayed detonation (red) and the violent merger model (dashed black) for different epochs after the explosion (indicated in the upper left of each panel). The spectral spread due to different viewing angles is shown for the maximum-light epochs of the two models in gamma rays (indicated in light red for the delayed detonation model in the third panel and in gray for the merger model in the fourth panel). Part of the effect is obscured by Monte Carlo noise in particular in the continuum. This problem is largely removed by using hardness ratios and broadband light curves. The ⁵⁶Ni and ⁵⁶Co emission lines are indicated in the first panel, and the flux bands C₁, L₁, and L₂ discussed in Sect. 3.2 are depicted in the second panel.