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Discovery and Follow-up Observations of the Young Type Ia Supernova 2016coj

  • Author(s): Zheng, W
  • Filippenko, AV
  • Mauerhan, J
  • Graham, ML
  • Yuk, H
  • Hosseinzadeh, G
  • Silverman, JM
  • Rui, L
  • Arbour, R
  • Foley, RJ
  • Abolfathi, B
  • Abramson, LE
  • Arcavi, I
  • Barth, AJ
  • Bennert, VN
  • Brandel, AP
  • Cooper, MC
  • Cosens, M
  • Fillingham, SP
  • Fulton, BJ
  • Halevi, G
  • Howell, DA
  • Hsyu, T
  • Kelly, PL
  • Kumar, S
  • Li, L
  • Li, W
  • Malkan, MA
  • Manzano-King, C
  • McCully, C
  • Nugent, PE
  • Pan, YC
  • Pei, L
  • Scott, B
  • Sexton, RO
  • Shivvers, I
  • Stahl, B
  • Treu, T
  • Valenti, S
  • Vogler, HA
  • Walsh, JL
  • Wang, X
  • et al.

The Type Ia supernova (SN Ia) 2016coj in NGC 4125 (redshift z = 0.00452 ± 0.00006) was discovered by the Lick Observatory Supernova Search 4.9 days after the fitted first-light time (FFLT; 11.1 days before B-band maximum). Our first detection (prediscovery) is merely 0.6 ± 0.5 days after the FFLT, making SN 2016coj one of the earliest known detections of an SN Ia. A spectrum was taken only 3.7 hr after discovery (5.0 days after the FFLT) and classified as a normal SN Ia. We performed high-quality photometry, low- and high-resolution spectroscopy, and spectropolarimetry, finding that SN 2016coj is a spectroscopically normal SN Ia, but the velocity of Si ii λ6355 around peak brightness (∼12,600 kms-1) is a bit higher than that of typical normal SNe. The Si ii λ6355 velocity evolution can be well fit by a broken-power-law function for up to a month after the FFLT. SN 2016coj has a normal peak luminosity (MB ≈ -18.9 ± 0.2 mag), and it reaches a B-band maximum ∼16.0 days after the FFLT. We estimate there to be low host-galaxy extinction based on the absence of Na i D absorption lines in our low- and high-resolution spectra. The spectropolarimetric data exhibit weak polarization in the continuum, but the Si ii line polarization is quite strong (∼0.9% ± 0.1%) at peak brightness.

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