Characterizing the secondary maximum in the r-band for Type Ia supernovae: diagnostic for the ejecta mass

An increase in the number of studied Type Ia supernovae (SNe Ia) has demonstrated that this class of explosions has a greater diversity in its observables than was previously assumed. The reasons (e.g. the explosion mechanism, progenitor system) for such a diversity remain unknown. Here, we analyse a sample of r-band light curves of SNe Ia, focusing on their behaviour similar to 2-4 weeks after maximum light, i.e. the second maximum. We characterize the second maximum by its timing (t(r2)) and the integrated flux ((F) over bar (r2)). We find that t(r2) correlates with the 'colour-stretch' parameter s(BV), which can be used as a proxy for Ni-56 mass, and (F) over bar (r2) correlates with the transparency time-scale, t(0). Using (F) over bar (r2) for a sample of 199 SNe from the Palomar Transient Factory and intermediate Palomar Transient Factory, we evaluate a distribution on t(0) for a sample of SNe Ia found in an 'untargeted' survey. Comparing this distribution to the predictions of t(0) ranges from models we find that the largest overlap in t(0) values between models and observations is for the sub-Chandrasekhar double detonation models. We also compare our relations between t(0) and (F) over bar (r2) with that from the 1D explosion models of Goldstein & Kasen and confirm that (F) over bar (r2) can be used as a diagnostic of the total ejecta mass.