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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2017
- DOI:
- 10.3847/1538-4357/835/1/13
- arXiv:
- arXiv:1608.02994
- Bibcode:
- 2017ApJ...835...13J
- Keywords:
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- nuclear reactions;
- nucleosynthesis;
- abundances;
- supernovae: general;
- supernovae: individual: SN 2007bi;
- LSQ14an;
- SN 2015bn;
- radiative transfer;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Published version