Optical Photometry of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex in IC 5179

TL;DR

This paper presents detailed optical lightcurves of two supernovae, highlighting the importance of precise calibration for cosmology and providing the first observation of shock breakout in a Type Ib/c supernova, supporting core-collapse origin.

Contribution

It offers high-quality lightcurves for SN 1999ee and SN 1999ex, demonstrates the necessity of accurate instrumental calibration, and reports the first shock breakout detection in a Type Ib/c supernova.

Findings

SN 1999ee's well-sampled lightcurve from -10 to +53 days.

Systematic photometric differences highlight calibration challenges.

First observed shock breakout in a Type Ib/c supernova, occurring 18 days before Bmax.

Abstract

We present UBVRIz lightcurves of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex, both located in the galaxy IC 5179. SN 1999ee has an extremely well sampled lightcurve spanning from 10 days before Bmax through 53 days after peak. Near maximum we find systematic differences ~0.05 mag in photometry measured with two different telescopes, even though the photometry is reduced to the same local standards around the supernova using the specific color terms for each instrumental system. We use models for our bandpasses and spectrophotometry of SN 1999ee to derive magnitude corrections (S-corrections) and remedy this problem. This exercise demonstrates the need of accurately characterizing the instrumental system before great photometric accuracies of Type Ia supernovae can be claimed. It also shows that this effect can have important astrophysical consequences since a small systematic shift of 0.02 mag in the B-V color can introduce a 0.08 mag error in the extinction corrected peak B magnitudes of a supernova and thus lead to biased cosmological parameters. The data for the Type Ib/c SN 1999ex present us with the first ever observed shock breakout of a supernova of this class. These observations show that shock breakout occurred 18 days before Bmax and support the idea that Type Ib/c supernovae are due to core collapse of massive stars rather than thermonuclear disruption of white dwarfs.