The detection efficiency of type Ia supernovae from the Zwicky Transient Facility: Limits on the intrinsic rate of early flux excesses

TL;DR

This study assesses the detection efficiency of early flux excesses in young type Ia supernovae using simulations of survey cadences, estimating the intrinsic rate of such excesses in the population.

Contribution

It provides the first quantitative analysis of detection efficiencies for early supernova flux excesses and estimates their intrinsic occurrence rate.

Findings

Only about 10-15% of supernovae are detected early enough to identify flux excesses in typical surveys.

Detection efficiency improves with shorter cadences, e.g., from 10% to 15% when reducing cadence from three to two days.

The intrinsic fraction of supernovae with early flux excesses is estimated to be around 28%.

Abstract

Samples of young type Ia supernovae have shown `early excess' emission in a few cases. Similar excesses are predicted by some explosion and progenitor scenarios and hence can provide important clues regarding the origin of thermonuclear supernovae. They are however, only predicted to last up to the first few days following explosion. It is therefore unclear whether such scenarios are intrinsically rare or if the relatively small sample size simply reflects the difficulty in obtaining sufficiently early detections. To that end, we perform toy simulations covering a range of survey depths and cadences, and investigate the efficiency with which young type Ia supernovae are recovered. As input for our simulations, we use models that broadly cover the range of predicted luminosities. Based on our simulations, we find that in a typical three day cadence survey, only $\sim$10% of type Ia supernovae would be detected early enough to rule out the presence of an excess. A two day cadence however, should see this increase to $\sim$15%. We find comparable results from more detailed simulations of the Zwicky Transient Facility surveys. Using the recovery efficiencies from these detailed simulations, we investigate the number of young type Ia supernovae expected to be discovered assuming some fraction of the population come from scenarios producing an excess at early times. Comparing the results of our simulations to observations, we find the intrinsic fraction of type Ia supernovae with early flux excesses is $\sim28^{+13}_{-11}%$%.