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Published January 20, 2017 | Accepted Version
Journal Article Open

Long-duration superluminous supernovae at late times

Abstract

Nebular-phase observations and spectral models of Type Ic superluminous supernovae (SLSNe) are presented. LSQ14an and SN 2015bn both display late-time spectra similar to galaxy-subtracted spectra of SN 2007bi, and the class shows strong similarity with broad-lined SNe Ic such as SN 1998bw. Near-infrared observations of SN 2015bn show a strong Ca II triplet, O I 9263, O I 1.13 μm, and Mg I 1.50 μm, but no distinct He, Si, or S emission. The high Ca II NIR/[Ca II] 7291, 7323 ratio of ~2 indicates a high electron density of n_e ≳ 10^8 cm−3. Spectral models of oxygen-zone emission are investigated to put constraints on the emitting region. Models require M(O-zone) ≳ 10 M⊙ to produce enough [O I] 6300, 6364 luminosity, irrespective of the powering situation and the density. The high oxygen-zone mass, supported by high estimated magnesium masses, points to explosions of massive CO cores, requiring M_(ZAMS) ≳ 40 M⊙. Collisions of pair-instability pulsations do not provide enough mass to account for the emission. [O II] and [O III] lines emerge naturally in many models, which strengthens the identification of broad [O II] 7320, 7330, [O III] 4363, and [O III] 4959, 5007 in some spectra. A small filling factor f ≾ 0.01 for the O/Mg zone is needed to produce enough luminosity in Mg I] 4571, Mg I 1.504 μm, and O I recombination lines, which shows that the ejecta is clumped. We review the constraints from the nebular spectral modeling in the context of the various scenarios proposed for SLSNe.

Additional Information

© 2017 The American Astronomical Society. Received 2016 August 9; revised 2016 November 28; accepted 2016 November 28; published 2017 January 16. We thank S. Blinnikov, C. Fransson, A. Kozyreva, P Mazzali, and C. Harris for discussion. A.J. thanks the organisers and participants of MIAPP conference "The Physics of Supernovae" and the workshop "Supernovae: The Outliers" for stimulating discussions. A.J. acknowledges funding by the European Union's Framework Programme for Research and Innovation Horizon 2020 under Marie Sklodowska-Curie grant agreement No 702538, and Science and Technology Facilities Council DIRAC computing grants ACSP45 and ACSP74. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERfC Grant agreement no [291222]. Agreements 307260, 320360, and 615929 are also acknowledged. SJS acknowledges funding from STFC grants ST/I001123/1 and ST/L000709/1. This work is based in part on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile as part of PESSTO, (the Public ESO Spectroscopic Survey for Transient Objects Survey) ESO program 188.D-3003, 191.D-0935 and on the VLT ESO Programmes 094.A-0645, 096.D-0191and 296.D-5042. K.M. acknowledges support from the STFC through an Ernest Rutherford Fellowship. S.T. acknowledges support by TRR 33 The Dark universe of the German Research Foundation. T.-W.C. and T.K. acknowledge the support through the Sofia Kovalevskaja Award to P. Schady from the Alexander von Humboldt Foundation of Germany. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. We have made use of the Weizmann interactive supernova data repository-http://wiserep.weizmann.ac.il. The Pan-STARRS1 Surveys (PS1) have been made possible through contributions of the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under Grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation under Grant No. AST-1238877, the University of Maryland, and Eotvos Lorand University (ELTE) and the Los Alamos National Laboratory.

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August 19, 2023
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October 20, 2023