Nebular spectra of pair-instability supernovae

A. Jerkstrand*, S. J. Smartt, A. Heger

*Corresponding author for this work

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

If very massive stars (M ≲ 100M⊙) can form and avoid too strong mass-loss during their evolution, they are predicted to explode as pair-instability supernovae (PISNe). One critical test for candidate events is whether their nucleosynthesis yields and internal ejecta structure, being revealed through nebular-phase spectra at t ≳ 1 yr, match those of model predictions. Here, we compute theoretical spectra based on model PISN ejecta at 1-3 yr post-explosion to allow quantitative comparison with observations. The high column densities of PISNe lead to complete gamma-ray trapping for t ≳ 2 yr which, combined with fulfilled conditions of steady state, leads to bolometric supernova luminosities matching the 56Co decay. Most of the gamma-rays are absorbed by the deep-lying iron and silicon/sulphur layers. The ionization balance shows a predominantly neutral gas state, which leads to emission lines of Fe I, Si I, and S I. For low-mass PISNe, the metal core expands slowly enough to produce a forest of distinct lines, whereas high-mass PISNe expand faster and produce more featureless spectra. Line blocking is complete below ~5000 Å for several years, and the model spectra are red. The strongest line is typically [Ca II] λλ7291, 7323, one of few lines from ionized species. We compare our models with proposed PISN candidates SN 2007bi and PTF12dam, finding discrepancies for several key observables and thus no support for a PISN interpretation. We discuss distinct spectral features predicted by the models, and the possibility of detecting pair-instability explosions among non-superluminous supernovae.

Original languageEnglish
Pages (from-to)3207-3229
Number of pages23
JournalMonthly Notices of the Royal Astronomical Society
Volume455
Issue number3
DOIs
Publication statusPublished - 26 Nov 2015

Keywords

  • Line: formation
  • Radiative transfer
  • Stars: evolution
  • Supernovae: general
  • Supernovae: individual: PTF12dam
  • Supernovae: individual: SN 2007bi

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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