Extended Data Fig. 6: The bolometric light curve of SN 2020eyj can be described with a radioactive decay model for the peak phase and an optically thick wind for the tail phase.

For the initial SN Ia peak of SN 2020eyj, we adopt the bolometric light curve (solid lines) accompanying the SN Ia template fit to the gri photometry (see ‘Light-curve fits’ section in Methods), assuming no line-of-sight extinction (in green) and an extinction of E(B − V) = 0.5 mag (in orange). Overplotted are the associated bolometrically corrected luminosities up to 40 days. From epoch 46 days onward, the SN Ia template fit no longer accurately describes the observed (g-band) photometry (Extended Data Fig. 1). The dotted lines show the continuation of the bolometric light curve of the underlying SN Ia. The three measurements in the tail phase are based on the integration of the two Keck spectra, extrapolated to the UV, and a bolometrically corrected photometric ALFOSC epoch. The dashed lines represent the fits to the tail-phase measurements using the analytical model from ref. ²⁶, following the same colour scheme for the level of extinction. In the transition region from the diffusion peak to the CSM-interaction-powered tail, between 50 and 100 days, the sum of the models would overestimate the luminosity, suggesting that the CSM configuration is more complicated than a simple wind-like density profile. The red diamonds show the infrared luminosity of SN 2020eyj (Extended Data Table 3), which are not included in the model fits.