2025MNRAS.540.3247S

Type Ia supernovae (SNe Ia) are widely believed to arise from thermonuclear explosions of white dwarfs (WDs). However, ongoing debate surrounds their progenitor systems and the mechanisms triggering these explosions. Recently, Sharon & Kushnir showed that existing models do not reproduce the observed positive correlation between the $\gamma$-ray escape time, $t_0$, and the synthesized $^{56}$Ni mass, $M_\mathrm{Ni56}$. Their analysis, while avoiding complex radiation transfer (RT) calculations, did not account for the viewing-angle dependence of the derived $t_0$ and $M_\mathrm{Ni56}$ in multidimensional (multi-D) models during pre-nebular phases, where most observations performed. Here, we aim to identify an observational width-luminosity relation, similar to the $t_0$-$M_\mathrm{Ni56}$ relation to constrain multi-D models during pre-nebular phases while minimizing RT calculation uncertainties. We show that the bolometric luminosity at $t\le 30$ d since explosion can be accurately computed without non-thermal ionization considerations, which are computationally expensive and uncertain. We find that the ratio of the bolometric luminosity at 30 d since explosion to the peak luminosity, $L_{30}/Lp$, correlates strongly with $t_0$. Using a sample of well-observed SNe Ia, we show that this parameter tightly correlates with the peak luminosity, $L_\mathrm{ p}$. We compare the observed $L_{30}/Lp$-$L_\mathrm{ p}$ distribution with models from the literature, including non-spherical models consisting of head-on WD collisions and off-centred ignitions of sub-Chandrasekhar mass WDs. We find that all known SNe Ia models fail to reproduce the observed bolometric luminosity-width correlation.