Two classes of fast-declining Type Ia supernovae

¹ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
e-mail: sdhawan@eso.org
² Excellence Cluster Universe, Technische Universität München, Boltzmannstrasse 2, 85748 Garching, Germany
³ Physik Department, Technische Universität München, James-Franck-Strasse 1, 85748 Garching bei München, Germany
⁴ Aix Marseille Université, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, 13013 Marseille, France

Received: 27 September 2016
Accepted: 15 February 2017

Abstract

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 < 0.3× 10⁴³ erg s^-1 are spectroscopically classified as 91bg-like and show only a single NIR peak. SNe with L_max > 0.5× 10⁴³ erg s^-1 appear to smoothly connect to normal SN Ia. The total ejecta mass (M_ej) values for SNe with enough late time data are ≲1 M_⊙, indicating a sub-Chandrasekhar mass progenitor for these SNe.