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

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


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 (σnoise ∼ σ int ∼ 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 MHe=0.01 M⊙) 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.

Original languageEnglish (US)
Article number48
JournalAstrophysical Journal
Issue number1
StatePublished - Oct 10 2020

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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  • ZTF early observations of type Ia supernovae. III.

    Bulla, M. (Creator), Miller, A. A. (Creator), Yao, Y. (Creator), Dessart, L. (Creator), Dhawan, S. (Creator), Papadogiannakis, S. (Creator), Biswas, R. (Creator), Goobar, A. (Creator), Kulkarni, S. R. (Creator), Nordin, J. (Creator), Nugent, P. (Creator), Polin, A. (Creator), Sollerman, J. (Creator), Bellm, E. C. (Creator), Coughlin, M. W. (Creator), Dekany, R. (Creator), Golkhou, V. Z. (Creator), Graham, M. J. (Creator), Kasliwal, M. M. (Creator), Kupfer, T. (Creator), Laher, R. R. (Creator), Masci, F. J. (Creator), Porter, M. (Creator), Rusholme, B. (Creator) & Shupe, D. L. (Creator), Centre de Donnees Strasbourg (CDS), 2022


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