The Subluminous Supernova 2007qd: A Missing Link in a Family of Low-Luminosity Type Ia Supernovae

TL;DR

SN 2007qd is a highly subluminous Type Ia supernova with intermediate properties, providing insights into the diversity of SN Ia explosions and their connection to other peculiar and low-luminosity events.

Contribution

This paper reports detailed photometric and spectroscopic observations of SN 2007qd, highlighting its unique properties and suggesting it as a missing link within the SN 2002cx-like supernova family.

Findings

SN 2007qd had an extremely fast rise time of <= 10 days.

It reached a peak absolute B magnitude of -15.4, making it one of the most subluminous SN Ia.

Its photospheric velocity was only 2800 km/s near maximum brightness.

Abstract

We present multi-band photometry and multi-epoch spectroscopy of the peculiar Type Ia supernova (SN Ia) 2007qd, discovered by the SDSS-II Supernova Survey. It possesses physical properties intermediate to those of the peculiar SN 2002cx and the extremely low-luminosity SN 2008ha. Optical photometry indicates that it had an extraordinarily fast rise time of <= 10 days and a peak absolute B magnitude of -15.4 +/- 0.2 at most, making it one of the most subluminous SN Ia ever observed. Follow-up spectroscopy of SN 2007qd near maximum brightness unambiguously shows the presence of intermediate-mass elements which are likely caused by carbon/oxygen nuclear burning. Near maximum brightness, SN 2007qd had a photospheric velocity of only 2800 km/s, similar to that of SN 2008ha but about 4000 and 7000 km/s less than that of SN 2002cx and normal SN Ia, respectively. We show that the peak luminosities of SN 2002cx-like objects are highly correlated with both their light-curve stretch and photospheric velocities. Its strong apparent connection to other SN 2002cx-like events suggests that SN 2007qd is also a pure deflagration of a white dwarf, although other mechanisms cannot be ruled out. It may be a critical link between SN 2008ha and the other members of the SN 2002cx-like class of objects.