2018ApJ...852L..33G

There are two classes of viable progenitors for normal Type Ia supernovae (SNe Ia): systems in which a white dwarf explodes at the Chandrasekhar mass (M_ch), and systems in which a white dwarf explodes below the Chandrasekhar mass (sub-M_ch). It is not clear which of these channels is dominant; observations and light-curve modeling have provided evidence for both. Here we use an extensive grid of 4500 time-dependent, multiwavelength radiation transport simulations to show that the sub-M_ch model can reproduce the entirety of the width-luminosity relation, while the M_ch model can only produce the brighter events (0.8 ΔM₁₅(B) 1.55), implying that fast-declining SNe Ia come from sub-M_ch explosions. We do not assume a particular theoretical paradigm for the progenitor or explosion mechanism, but instead construct parameterized models that vary the mass, kinetic energy, and compositional structure of the ejecta, thereby realizing a broad range of possible outcomes of white dwarf explosions. We provide fitting functions based on our large grid of detailed simulations that map observable properties of SNe Ia, such as peak brightness and light-curve width, to physical parameters such as ⁵⁶Ni and total ejected mass. These can be used to estimate the physical properties of observed SNe Ia.