Long-duration Superluminous Supernovae at Late Times

A. Jerkstrand, S. J. Smartt, C. Inserra, M. Nicholl, T.-W. Chen, T. Krühler, J. Sollerman, S. Taubenberger, A. Gal-Yam, E. Kankare, K. Maguire, M. Fraser, S. Valenti, M. Sullivan, R. Cartier, D. R. Young

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43 Citations (Scopus)

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.
Original languageEnglish
Pages (from-to)13
JournalThe Astrophysical Journal
Volume835
Issue number1
DOIs
Publication statusPublished - 16 Jan 2017

Keywords

  • nuclear reactions
  • nucleosynthesis
  • abundances
  • supernovae: general
  • supernovae: individual: SN 2007bi
  • LSQ14an
  • SN 2015bn
  • radiative transfer

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