On the Rates of Type Ia Supernovae in Dwarf and Giant Hosts with ROTSE-IIIb

TL;DR

This study measures the local rate of Type Ia supernovae using ROTSE-IIIb data, revealing a higher rate than previously thought and highlighting potential undercounting of faint or host-faint supernovae.

Contribution

It provides a new estimate of the local Type Ia supernova rate based on ROTSE-IIIb observations and compares different supernova luminosity distributions.

Findings

The supernova rate is more than double the canonical value.

A significant number of SNeIa are found in very low-luminosity galaxies.

The pseudo-absolute magnitude distribution from LOSS is incompatible with SDSS-II data.

Abstract

We present a sample of 23 spectroscopically confirmed Type Ia supernovae that were discovered in the background of galaxy clusters targeted by ROTSE-IIIb and use up to 18 of these to determine the local (z = 0.05) volumetric rate. Since our survey is flux limited and thus biased against fainter objects, the pseudo-absolute magnitude distribution (pAMD) of SNeIa in a given volume is an important concern, especially the relative frequency of high to low-luminosity SNeIa. We find that the pAMD derived from the volume limited Lick Observatory Supernova Search (LOSS) sample is incompatible with the distribution of SNeIa in a volume limited (z<0.12) sub sample of the SDSS-II. The LOSS sample requires far more low-luminosity SNeIa than the SDSS-II can accommodate. Even though LOSS and SDSS-II have sampled different SNeIa populations, their volumetric rates are surprisingly similar. Using the same model pAMD adopted in the SDSS-II SNeIa rate calculation and excluding two high-luminosity SNeIa from our sample, we derive a rate that is marginally higher than previous low-redshift determinations. With our full sample and the LOSS pAMD our rate is more than double the canonical value. We also find that 5 of our 18 SNeIa are hosted by very low-luminosity (M_B > -16) galaxies, whereas only 1 out 79 nearby SDSS-II SNeIa have such faint hosts. It is possible that previous works have under-counted either low luminosity SNeIa, SNeIa in low luminosity hosts, or peculiar SNeIa (sometimes explicitly), and the total SNeIa rate may be higher than the canonical value.