{
  "id": "2001.00598",
  "version": "v1",
  "published": "2020-01-02T19:13:58.000Z",
  "updated": "2020-01-02T19:13:58.000Z",
  "title": "ZTF Early Observations of Type Ia Supernovae II: First Light, the Initial Rise, and Time to Reach Maximum Brightness",
  "authors": [
    "A. A. Miller",
    "Y. Yao",
    "M. Bulla",
    "E. C. Bellm",
    "S. B. Cenko",
    "R. Dekany",
    "C. Fremling",
    "M. J. Graham",
    "T. Kupfer",
    "R. R. Laher",
    "A. A. Mahabal",
    "F. J. Masci",
    "P. E. Nugent",
    "R. Riddle",
    "B. Rusholme",
    "R. M. Smith",
    "D. L. Shupe",
    "J. van Roestel",
    "S. R. Kulkarni"
  ],
  "comment": "29 pages, 16 figures; submitted to ApJ; comments are welcome",
  "categories": [
    "astro-ph.HE"
  ],
  "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 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 ($\\alpha_r = 2.01\\pm0.02$), 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.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-01-02T19:13:58.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "type ia supernovae",
      "reach maximum brightness",
      "ztf early observations",
      "synoptic survey telescope observations",
      "initial rise"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 29,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}