Two classes of fast-declining type Ia supernovae

Abstract

Fast-declining Type Ia supernovae (SN Ia) separate into two categories based on their bolometric and near-infrared (NIR) properties. The peak bolometric luminosity (${\mathrm{L}}_{\max }$), 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 (${\mathrm{L}}_{\max }$ differing by up to a factor of $\sim$ 8). All fast-declining SN Ia with ${\mathrm{L}}_{\max }<0.3\cdot$ 10${}^{43}{\mathrm{ergs}}^{-1}$ are spectroscopically classified as 91bg-like and show only a single NIR peak. SNe with ${\mathrm{L}}_{\max }>0.5\cdot$ 10${}^{43}{\mathrm{ergs}}^{-1}$ appear to smoothly connect to normal SN Ia. The total ejecta mass (M${}_{ej}$) values for SNe with enough late time data are $\lesssim$1 $M_{\odot }$, indicating a sub-Chandrasekhar mass progenitor for these SNe.

8 pages, 3 figures; Accepted for publication in A&A