ZTF Early Observations of Type Ia Supernovae. III. Early-time Colors As a Test for Explosion Models and Multiple Populations

October 2020 • 2020ApJ...902...48B

Authors • Bulla, Mattia • Miller, Adam A. • Yao, Yuhan • Dessart, Luc • Dhawan, Suhail • Papadogiannakis, Semeli • Biswas, Rahul • Goobar, Ariel • Kulkarni, S. R. • Nordin, Jakob • Nugent, Peter • Polin, Abigail • Sollerman, Jesper • Bellm, Eric C. • Coughlin, Michael W. • Dekany, Richard • Golkhou, V. Zach • Graham, Matthew J. • Kasliwal, Mansi M. • Kupfer, Thomas • Laher, Russ R. • Masci, Frank J. • Porter, Michael • Rusholme, Ben • Shupe, David L.

Abstract • Colors of Type Ia supernovae (SNe Ia) in the first few days after explosion provide a potential discriminant between different models. In this paper, we present g - r colors of 65 SNe Ia discovered within 5 days from first light by the Zwicky Transient Facility in 2018, a sample that is about three times larger than that in the literature. We find that g - r colors are intrinsically rather homogeneous at early phases, with about half of the dispersion attributable to photometric uncertainties ( ${\sigma }_{\mathrm{noise}}\sim {\sigma }_{\mathrm{int}}\,\sim $ 0.18 mag). Colors are nearly constant starting from 6 days after first light (g - r ∼ -0.15 mag), while the time evolution at earlier epochs is characterized by a continuous range of slopes, from events rapidly transitioning from redder to bluer colors (slope of ∼-0.25 mag day^-1) to events with a flatter evolution. The continuum in the slope distribution is in good agreement both with models requiring some amount of ⁵⁶Ni mixed in the outermost regions of the ejecta and with "double-detonation" models having thin helium layers ( ${M}_{\mathrm{He}}=0.01\,{M}_{\odot }$ ) and varying carbon-oxygen core masses. At the same time, six events show evidence for a distinctive "red bump" signature predicted by double-detonation models with larger helium masses. We finally identify a significant correlation between the early-time g - r slopes and supernova brightness, with brighter events associated to flatter color evolution (p-value = 0.006). The distribution of slopes, however, is consistent with being drawn from a single population, with no evidence for two components as claimed in the literature based on B - V colors.

Links

• PREPRINT http://arxiv.org/abs/2001.00587
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2020ApJ...902...48B
• ELECTR https://doi.org/10.3847%2F1538-4357%2Fabb13c
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2020ApJ...902...48B
• PDF https://iopscience.iop.org/article/10.3847/1538-4357/abb13c/pdf
• PDF https://stacks.iop.org/0004-637X/902/48/pdf
• DATA http://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/902/48