2017A&A...602A.118D

We aim to characterise a sample of fast-declining Type Ia supernovae (SN Ia) using their bolometric and near-infrared (NIR) properties. Based on these properties, we find that fast-declining SN Ia separate into two categories based on their bolometric and NIR properties. The peak bolometric luminosity (L_max), the phase of the first maximum relative to the optical, the NIR peak luminosity, and the occurrence of a second maximum in the NIR distinguish a group of very faint SN Ia. Fast-declining supernovae show a large range of peak bolometric luminosities (L_max differing by up to a factor of ∼8). All fast-declining SN Ia with L_max<0.3x 10⁴³erg/s are spectroscopically classified as 91bg-like and show only a single NIR peak. SNe with L_max>0.5x10⁴³erg/s appear to smoothly connect to normal SN Ia. The total ejecta mass (M_ej) values for SNe with enough late time data are ≤1M_☉, indicating a sub-Chandrasekhar mass progenitor for these SNe.