ZTF Early Observations of Type Ia Supernovae II: First Light, the Initial Rise, and Time to Reach Maximum Brightness. (arXiv:2001.00598v1 [astro-ph.HE])

ZTF Early Observations of Type Ia Supernovae II: First Light, the Initial Rise, and Time to Reach Maximum Brightness. (arXiv:2001.00598v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Miller_A/0/1/0/all/0/1">A. A. Miller</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yao_Y/0/1/0/all/0/1">Y. Yao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bulla_M/0/1/0/all/0/1">M. Bulla</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bellm_E/0/1/0/all/0/1">E. C. Bellm</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cenko_S/0/1/0/all/0/1">S. B. Cenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dekany_R/0/1/0/all/0/1">R. Dekany</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fremling_C/0/1/0/all/0/1">C. Fremling</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Graham_M/0/1/0/all/0/1">M. J. Graham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kupfer_T/0/1/0/all/0/1">T. Kupfer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Laher_R/0/1/0/all/0/1">R. R. Laher</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mahabal_A/0/1/0/all/0/1">A. A. Mahabal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Masci_F/0/1/0/all/0/1">F. J. Masci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nugent_P/0/1/0/all/0/1">P. E. Nugent</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Riddle_R/0/1/0/all/0/1">R. Riddle</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rusholme_B/0/1/0/all/0/1">B. Rusholme</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_R/0/1/0/all/0/1">R. M. Smith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shupe_D/0/1/0/all/0/1">D. L. Shupe</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Roestel_J/0/1/0/all/0/1">J. van Roestel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kulkarni_S/0/1/0/all/0/1">S. R. Kulkarni</a>

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 unique, and large,
data set of 127 SNe Ia with exquisite coverage by the Zwicky Transient Facility
(ZTF). High-cadence (6 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 the mean power-law index is consistent with 2 in the
$r_mathrm{ztf}$-band ($alpha_r = 2.01pm0.02$), 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 18.5$,$d (with
a range extending from $sim$15$-$22$,$d), 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 $alpha=2$, in which case we estimate a mean rise
time of 21.0$,$d (with a range from $sim$18$-$23$,$d). The sample includes a
handful or rare and peculiar SNe Ia. Finally, we conclude with a discussion of
lessons learned from the ZTF sample that can eventually be applied to Large
Synoptic Survey Telescope observations.

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 unique, and large,
data set of 127 SNe Ia with exquisite coverage by the Zwicky Transient Facility
(ZTF). High-cadence (6 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 the mean power-law index is consistent with 2 in the
$r_mathrm{ztf}$-band ($alpha_r = 2.01pm0.02$), 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 18.5$,$d (with
a range extending from $sim$15$-$22$,$d), 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 $alpha=2$, in which case we estimate a mean rise
time of 21.0$,$d (with a range from $sim$18$-$23$,$d). The sample includes a
handful or rare and peculiar SNe Ia. Finally, we conclude with a discussion of
lessons learned from the ZTF sample that can eventually be applied to Large
Synoptic Survey Telescope observations.

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