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Long-duration superluminous supernovae at late times

Jerkstrand, A., Smartt, S. J., Inserra, C., Nicholl, M., Chen, T.-W., Krühler, T., Sollerman, J., Taubenberger, S., Gal-Yam, A., Kankare, E., Maguire, K., Fraser, M., Valenti, S., Sullivan, M., Cartier, R. and Young, D. R. 2017. Long-duration superluminous supernovae at late times. Astrophysical Journal 835 (1) , 13. 10.3847/1538-4357/835/1/13

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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 ${n}_{e}\gtrsim {10}^{8}$ cm−3. Spectral models of oxygen-zone emission are investigated to put constraints on the emitting region. Models require $M({\rm{O}} \mbox{-} \mathrm{zone})\gtrsim 10$ 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 ${M}_{\mathrm{ZAMS}}\gtrsim 40\,{M}_{\odot }$. 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 $f\lesssim 0.01$ 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.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: American Astronomical Society
ISSN: 0004-637X
Date of First Compliant Deposit: 23 January 2019
Date of Acceptance: 28 November 2016
Last Modified: 31 Jan 2019 11:30
URI: http://orca.cf.ac.uk/id/eprint/118670

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