ZTF Early Observations of Type Ia Supernovae. II. First Light, the Initial Rise, and Time to Reach Maximum Brightness

October 2020 • 2020ApJ...902...47M

Authors • Miller, A. A. • Yao, Y. • Bulla, M. • Pankow, C. • Bellm, E. C. • Cenko, S. B. • Dekany, R. • Fremling, C. • Graham, M. J. • Kupfer, T. • Laher, R. R. • Mahabal, A. A. • Masci, F. J. • Nugent, P. E. • Riddle, R. • Rusholme, B. • Smith, R. M. • Shupe, D. L. • van Roestel, J. • Kulkarni, S. R.

Abstract • While it is clear that Type Ia supernovae (SNe) are the result of thermonuclear explosions in C/O white dwarfs (WDs), a great deal remains uncertain about the binary companion that facilitates the explosive disruption of the WD. Here, we present a comprehensive analysis of a large, unique data set of 127 SNe Ia with exquisite coverage by the Zwicky Transient Facility (ZTF). High-cadence (six observations per night) ZTF observations allow us to measure the SN rise time and examine its initial evolution. We develop a Bayesian framework to model the early rise as a power law in time, which enables the inclusion of priors in our model. For a volume-limited subset of normal SNe Ia, we find that the mean power-law index is consistent with 2 in the r_ZTF-band ( ${\alpha }_{r}=2.01\pm 0.02$ ), as expected in the expanding fireball model. There are, however, individual SNe that are clearly inconsistent with ${\alpha }_{r}=2$ . We estimate a mean rise time of 18.9 days (with a range extending from ∼15 to 22 days), though this is subject to the adopted prior. We identify an important, previously unknown, bias whereby the rise times for higher-redshift SNe within a flux-limited survey are systematically underestimated. This effect can be partially alleviated if the power-law index is fixed to α = 2, in which case we estimate a mean rise time of 21.7 days (with a range from ∼18 to 23 days). The sample includes a handful of rare and peculiar SNe Ia. Finally, we conclude with a discussion of lessons learned from the ZTF sample that can eventually be applied to observations from the Vera C. Rubin Observatory.

Links

• PREPRINT http://arxiv.org/abs/2001.00598
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2020ApJ...902...47M
• ELECTR https://doi.org/10.3847%2F1538-4357%2Fabb13b
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2020ApJ...902...47M
• PDF https://iopscience.iop.org/article/10.3847/1538-4357/abb13b/pdf
• PDF https://stacks.iop.org/0004-637X/902/47/pdf
• DATA http://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/902/47