Affiliations

Las Cumbres Observatory, Goleta, 93117, California, USA Iair Arcavi, D. Andrew Howell, Griffin Hosseinzadeh, Curtis McCully, Zheng Chuen Wong, Sarah Rebekah Katz & David Guevel Kavli Institute for Theoretical Physics, University of California, Santa Barbara, 93106, California, USA Iair Arcavi & Lars Bildsten Department of Physics, University of California, Santa Barbara, 93106, California, USA Iair Arcavi, D. Andrew Howell, Lars Bildsten, Griffin Hosseinzadeh, Curtis McCully, Zheng Chuen Wong, Sarah Rebekah Katz & David Guevel Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, 94720, California, USA Daniel Kasen Department of Physics, University of California, Berkeley, 94720, California, USA Daniel Kasen Department of Astronomy, University of California, Berkeley, 94720-3411, California, USA Daniel Kasen, Peter E. Nugent, Melissa L. Graham, Ken J. Shen & Alexei V. Filippenko Department of Particle Physics and Astrophysics, The Weizmann Institute of Science, Rehovot, 76100, Israel Avishay Gal-Yam, Giorgos Leloudas, Assaf Horesh, Eran O. Ofek, Ofer Yaron & Danny Khazov Department of Astronomy, The Oskar Klein Centre, Stockholm University, AlbaNova, SE-10691, Stockholm, Sweden Jesper Sollerman, Francesco Taddia, Christoffer Fremling & Anders Nyholm Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries vej 30, Copenhagen, 2100, Denmark Giorgos Leloudas & Daniel A. Perley Computational Research Division, Lawrence Berkeley National Laboratory, Berkeley, 94720, California, USA Peter E. Nugent Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, 91904, Israel Assaf Horesh & Nir J. Shaviv Department of Physics, Astrophysics, University of Oxford, Denys Wilkinson Building, Oxford, OX1 3RH, UK Kunal Mooley & Rob Fender Astrophysics Group, Cavendish Laboratory, 19 J. J. Thomson Avenue, Cambridge, CB3 0HE, UK Clare Rumsey Astrophysics Science Division, NASA Goddard Space Flight Center, Code 661, Greenbelt, 20771, Maryland, USA S. Bradley Cenko Joint Space-Science Institute, University of Maryland, College Park, 20742, Maryland, USA S. Bradley Cenko Department of Astronomy, University of Washington, Box 351580, Seattle, 98195-1580, Washington, USA Melissa L. Graham & Yi Cao Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool, L3 5RF, UK Daniel A. Perley The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv, 69978, Israel Ehud Nakar & Omer Bromberg eScience Institute, University of Washington, Box 351570, Seattle, 98195-1580, Washington, USA Yi Cao Physics Department and Tsinghua Center for Astrophysics, Tsinghua University, Beijing, 100084, China Xiaofeng Wang, Fang Huang, Liming Rui, Wenxiong Li & Zhitong Li Key Laboratory of Optical Astronomy, National Astronomical Observatories of China, Chinese Academy of Sciences, Beijing, 100012, China Tianmeng Zhang School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, 101408, China Tianmeng Zhang Yunnan Observatories, Chinese Academy of Sciences, Kunming, 650011, China Jujia Zhang Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Phoenix Mountain, East District, Kunming, 650216, Yunnan, China Jujia Zhang Department of Physics, University of California, 1 Shields Avenue, Davis, 95616, California, USA Stefano Valenti Carnegie Observatories, 813 Santa Barbara Street, Pasadena, 91101, California, USA Benjamin Shappee & Nick Konidaris Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, 43210, Ohio, USA Christopher S. Kochanek & Thomas W.-S. Holoien Center for Cosmology and AstroParticle Physics (CCAPP), The Ohio State University, 191 W. Woodruff Avenue, Columbus, 43210, Ohio, USA Christopher S. Kochanek & Thomas W.-S. Holoien Miller Institute for Basic Research in Science, University of California, Berkeley, 94720, California, USA Alexei V. Filippenko Cahill Center for Astrophysics, California Institute of Technology, Pasadena, 91125, California, USA Mansi M. Kasliwal, Nadja Blagorodnova, Richard S. Walters & Ragnhild Lunnan Department of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK Mark Sullivan Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218, Victoria, 3122, Australia Igor Andreoni ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), Australia Igor Andreoni Australian Astronomical Observatory, PO Box 915, North Ryde, 1670, New South Wales, Australia Igor Andreoni Spitzer Science Center, California Institute of Technology, MS 314-6, Pasadena, 91125, California, USA Russ R. Laher Space and Atmospheric Sciences Group, Mail Stop D466, Los Alamos National Laboratory, Los Alamos, 87545, New Mexico, USA Przemek Wozniak Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, 91109, USA Brian Bue

Contributions

I. Arcavi initiated the study, triggered follow-up observations, reduced data, performed the analysis and wrote the manuscript. D.A.H. is the Principal Investigator of the Las Cumbres Observatory (LCO) Supernova Key Project through which all of the LCO data were obtained; he also assisted with interpretation and the manuscript. D. Kasen and L.B. assisted with theoretical models, data interpretation, and with the manuscript. G.H. and C.McC. assisted with obtaining and reducing LCO data. Z.C.W. first flagged the supernova as interesting. S.R.K. performed the spectral expansion velocity measurements. A.G.-Y. is the Principal Investigator for core-collapse supernovae in iPTF and assisted with interpretation. J.S. and F.T. obtained the Nordic Optical Telescope spectra and polarimetry data and assisted with the manuscript. G.L. reduced the polarimetry data. C.F. reduced the Palomar 60-inch telescope (P60) data. P.E.N. discovered the 1954 eruption image of iPTF14hls, helped obtain the host-galaxy spectrum, and is a Co-Principal Investigator of the Keck proposal under which it and one of the supernova spectra were obtained. A.H. obtained and reduced the Very Large Array (VLA) data and is Principal Investigator of the programme through which the data were obtained. K.M. and C.R. obtained and reduced the Arcminute Microkelvin Imager Large Array (AMI-LA) data. S.B.C. obtained and reduced the Swift X-Ray Telescope (XRT) data. M.L.G. obtained and reduced Keck spectra. D.A.P. performed the host-galaxy analysis and assisted with the manuscript. E.N., O.B., N.J.S. and K.J.S. assisted with theoretical interpretation and the manuscript. E.O.O. helped with interpretation and the manuscript. Y.C. built the real-time iPTF image-subtraction pipeline and obtained Palomar 200-inch telescope (P200) observations. X.W., F.H., L.R., T.Z., W.L., Z.L. and J.Z. obtained and reduced the Xinglong, Lijiang, and Tsinghua University-NAOC telescope (TNT) data. S.V. built the LCO photometric and spectroscopic reduction pipelines and assisted with LCO observations, interpretation, and the manuscript. D.G. assisted with the Palomar Observatory Sky Survey (POSS) image analysis. B.S., C.S.K. and T.W.-S.H. obtained and reduced the All Sky Automated Survey for Supernovae (ASAS-SN) pre-discovery limits. A.V.F. is a Co-Principal Investigator of the Keck proposal under which the host-galaxy spectrum and one of the supernova spectra were obtained; he also helped with the manuscript. R.F. is Principal Investigator of the programme through which the AMI-LA data were obtained. A.N. helped scan for iPTF candidates and assisted with the manuscript. O.Y. is in charge of the iPTF candidate scanning effort. M.M.K. led the work for building iPTF. M.S. wrote the pipeline used to reduce Palomar 48-inch Oschin Schmidt telescope (P48) data. N.B. and R.S.W. obtained P60 SEDM photometry. R.L., D. Khazov, and I. Andreoni obtained P200 observations. R.R.L. contributed to building the P48 image-processing pipeline. N.K. was a main builder of the P60 SEDM. P.W. and B.B. helped build the machine-learning algorithms that identify iPTF supernova candidates.

Corresponding author

Correspondence to Iair Arcavi.