Type II supernovae are the final stage of massive stars (above 8 M⊙) which retain part of their hydrogen-rich envelope at the moment of explosion. They typically eject up to 15 M⊙ of material, with peak magnitudes of −17.5 mag and energies in the order of 1051 erg, which can be explained by neutrino-driven explosions and neutron star formation. Here, we present our study of OGLE-2014-SN-073, one of the brightest type II supernovae ever discovered, with an unusually broad lightcurve combined with high ejecta velocities. From our hydrodynamical modelling, we infer a remarkable ejecta mass of M⊙ and a relatively high explosion energy of erg. We show that this object belongs, along with a very small number of other hydrogen-rich supernovae, to an energy regime that is not explained by standard core-collapse neutrino-driven explosions. We compare the quantities inferred by the hydrodynamical modelling with the expectations of various exploding scenarios and attempt to explain the high energy and luminosity released. We find some qualitative similarities with pair-instability supernovae, although the prompt injection of energy by a magnetar seems to be a viable alternative explanation for such an extreme event.
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We thank M. Kubiak and G. Pietrzyn′ski—former members of the OGLE team—for contributions to the collection of the OGLE photometric data. G.T., S.B., E.C., N.E.-R., A.P. and M.T. are partially supported by PRIN–INAF 2014 with the project ‘Transient Universe: unveiling new types of stellar explosions with PESSTO’. N.E.-R. acknowledges financial support from MIUR PRIN 2010–2011, ‘The dark Universe and the cosmic evolution of baryons: from current surveys to Euclid’. G.T. is also supported by the fellowship for the study of bright type II supernovae, offered by INAF–OaPD. S.J.S. acknowledges funding from EU/FP7-ERC grant agreement 291222 and Science and Technology Facilities Council of the United Kingdom grants ST/I001123/1 and ST/L000709/1. T.-W.C. acknowledges support through the Sofia Kovalevskaja Award to P. Schady from the Alexander von Humboldt Foundation of Germany. T.J.M. is supported by the Grant-in-Aid for Research Activity Start-up of the Japan Society for the Promotion of Science (16H07413). F.T. and J.S. acknowledge support from the Knut and Alice Wallenberg Foundation. M.F. acknowledges support from a Royal Society—Science Foundation Ireland University Research Fellowship. Ł.W. was supported by the Polish National Science Centre grant OPUS 2015/17/B/ST9/03167. D.A.H. and C.M. are supported by NSF 1313484. G.D. and M.S. acknowledge support from EU/FP7-ERC grant 615929 and the Weizmann-UK ‘Making Connections’ programme. A.G.-Y. is supported by EU/FP7 via ERC grant 307260, the Quantum Universe I-Core programme by the Israeli Committee for planning and funding and the Israel Science Foundation, and Kimmel and YeS awards. A.J. acknowledges funding by the European Union’s Framework Programme for Research and Innovation Horizon 2020 under Marie Sklodowska-Curie grant agreement 702538. K.M. acknowledges support from the Science and Technology Facilities Council of the United Kingdom through an Ernest Rutherford Fellowship. Z.K.-R. acknowledges support from ERC Consolidator Grant 647208. The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to A.U. This study is based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, as part of PESSTO (ESO programme IDs 197.D.1075, 191.D-0935 and 188.D-3003) and observations made with ESO telescopes at the Paranal Observatory under programme 096.D-0894(A). GEMINI spectra were obtained under the GS-2015A-Q-56 programme (Principal Investigator D.A.H.). We are grateful to the Istituto Nazionale di Fisica Nucleare—Laboratori Nazionali del Sud for the use of computer facilities. This project used public archival data from the DES. Funding for the DES projects was provided by the U.S. Department of Energy, U.S. National Science Foundation, Ministry of Science and Education of Spain, Science and Technology Facilities Council of the United Kingdom, Higher Education Funding Council for England, National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, Kavli Institute for Cosmological Physics at the University of Chicago, Center of Cosmology and Astro Particle Physics at Ohio State University, Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Brazilian National Council for Scientific and Technological Development, Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro, Financiadora de Estudos e Projetos, Ministry of Economy and Competitiveness (Spain), Deutsche Forschungsgemeinschaft (Germany) and the collaborating institutions in the DES, which are the Argonne National Laboratory, University of California Santa Cruz, University of Cambridge, Centro de Investigaciones Energéticas, Medioambientales y Technológicas in Madrid, University of Chicago, University College London, DES–Brazil Consortium, University of Edinburgh, ETH Zürich, Fermilab, University of Illinois, Institute of Space Sciences (Institute of Space Studies of Catalonia–Spanish National Research Council), Institute for High Energy Physics at the Universitat Autònoma de Barcelona, Lawrence Berkeley Laboratory, Ludwig Maximilian University of Munich and the associated Excellence Cluster Universe, University of Michigan, National Optical Astronomy Observatory, University of Nottingham, Ohio State University, University of Pennsylvania, University of Portsmouth, SLAC National Laboratory, Stanford University, University of Sussex and Texas A&M University. This paper is also based on observations from the Las Cumbres Observatory: we thank their staff for excellent assistance. IRAF is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy under cooperative agreement with the National Science Foundation.
Supplementary Figures 1–4, Supplementary Table 1, Supplementary Text and Supplementary References.