Characterising the secondary maximum in the r-band for Type Ia Supernovae: Diagnostic for the ejecta mass

Abstract

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 $\sim$ 2-4 weeks after maximum light, i.e. the second maximum. We characterise the second maximum by its timing ($t_{r_2}$) and the integrated flux (${\overline{\mathcal{F}}}_{r_2}$). We find that $t_{r_2}$ correlates with the "colour-stretch" parameter s${}_{BV}$, which can be used as a proxy for ${}^{56}$Ni mass, and ${\overline{\mathcal{F}}}_{r_2}$, correlates with the transparency timescale, t${}_0$. Using ${\overline{\mathcal{F}}}_{r_2}$, 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 ${\overline{\mathcal{F}}}_{r_2}$, with that from 1-D explosion models of \citet{GK18} and confirm that ${\overline{\mathcal{F}}}_{r_2}$, can be used as a diagnostic of the total ejecta mass.

8 pages, 9 figures and 12 pages of tables, Accepted MNRAS