SN 2016coi (ASASSN-16fp): An Energetic H-stripped Core-collapse Supernova from a Massive Stellar Progenitor with Large Mass Loss

G. Terreran, R. Margutti, D. Bersier, J. Brimacombe, D. Caprioli, P. Challis, R. Chornock, D. L. Coppejans, Subo Dong, C. Guidorzi, K. Hurley, R. Kirshner, G. Migliori, D. Milisavljevic, D. M. Palmer, J. L. Prieto, L. Tomasella, P. Marchant, A. Pastorello, B. J. ShappeeK. Z. Stanek, M. D. Stritzinger, S. Benetti, Ping Chen, L. Demarchi, N. Elias-Rosa, C. Gall, J. Harmanen, S. Mattila

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


We present comprehensive observations and analysis of the energetic H-stripped SN 2016coi (a.k.a. ASASSN-16fp), spanning the γ-ray through optical and radio wavelengths, acquired within the first hours to ∼420 days post explosion. Our observational campaign confirms the identification of He in the supernova (SN) ejecta, which we interpret to be caused by a larger mixing of Ni into the outer ejecta layers. By modeling the broad bolometric light curve, we derive a large ejecta-mass-to-kinetic-energy ratio (M ej ∼ 4-7 M o, E k ∼ (7-8) × 1051 erg). The small [Ca ii] λλ7291,7324 to [O i] λλ6300,6364 ratio (∼0.2) observed in our late-time optical spectra is suggestive of a large progenitor core mass at the time of collapse. We find that SN 2016coi is a luminous source of X-rays (L X > 1039 erg s-1 in the first ∼100 days post explosion) and radio emission (L 8.5 GHz ∼ 7 × 1027 erg s-1 Hz-1 at peak). These values are in line with those of relativistic SNe (2009bb, 2012ap). However, for SN 2016coi, we infer substantial pre-explosion progenitor mass loss with a rate M ∼ (1-2) × 10-4Myr-1 and a sub-relativistic shock velocity v sh ∼ 0.15c, which is in stark contrast with relativistic SNe and similar to normal SNe. Finally, we find no evidence for a SN-associated shock breakout γ-ray pulse with energy E γ > 2 × 1046 erg. While we cannot exclude the presence of a companion in a binary system, taken together, our findings are consistent with a massive single-star progenitor that experienced large mass loss in the years leading up to core collapse, but was unable to achieve complete stripping of its outer layers before explosion.

Original languageEnglish (US)
Article number147
JournalAstrophysical Journal
Issue number2
StatePublished - Oct 1 2019


  • supernovae: Individual (SN 2016coi, ASASSN-16fp)

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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