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Abstract We present three new spectra of the nearby Type Ia supernova (SN Ia) 2011fe covering ≈480–850 days after maximum light and show that the ejecta undergoes a rapid ionization shift at ∼500 days after explosion. The prominent Fe iii emission lines at ≈4600 Å are replaced with Fe i +Fe ii blends at ∼4400 Å and ∼5400 Å. The ≈7300 Å feature, which is produced by [Fe ii ]+[Ni ii ] at ≲400 days after explosion, is replaced by broad (≈±15,000 km s −1 ) symmetric [Ca ii ] emission. Models predict this ionization transition occurring ∼100 days later than what is observed, which we attribute to clumping in the ejecta. Finally, we use the nebular-phase spectra to test several proposed progenitor scenarios for SN 2011fe. Nondetections of H and He exclude nearby nondegenerate companions, [O i ] nondetections disfavor the violent merger of two white dwarfs, and the symmetric emission-line profiles favor a symmetric explosion.
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Seven Years of SN 2014C: A Multiwavelength Synthesis of an Extraordinary Supernova
Abstract SN 2014C was originally classified as a Type Ib supernova, but at phase ϕ = 127 days, post-explosion strong H α emission was observed. SN 2014C has since been observed in radio, infrared, optical and X-ray bands. Here we present new optical spectroscopic and photometric data spanning ϕ = 947–2494 days post-explosion. We address the evolution of the broadened H α emission line, as well as broad [O iii ] emission and other lines. We also conduct a parallel analysis of all publicly available multiwavelength data. From our spectra, we find a nearly constant H α FWHM velocity width of ∼2000 km s −1 that is significantly lower than that of other broadened atomic transitions (∼3000–7000 km s −1 ) present in our spectra ([O i ] λ 6300; [O iii ] λ λ 4959, 5007; He i λ 7065; [Ca ii ] λ λ 7291, 7324). The late radio data demand a fast forward shock (∼10,000 km s −1 at ϕ = 1700 days) in rarified matter that contrasts with the modest velocity of the H α . We propose that the infrared flux originates from a toroidal-like structure of hydrogen surrounding the progenitor system, while later emission at other wavelengths (radio, X-ray) likely originates predominantly from the reverse shock in the ejecta and the forward shock in the quasi-spherical progenitor He-wind. We propose that the H α emission arises in the boundary layer between the ejecta and torus. We also consider the possible roles of a pulsar and a binary companion.
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- PAR ID:
- 10347651
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 930
- Issue:
- 1
- ISSN:
- 0004-637X
- Page Range / eLocation ID:
- 57
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.3847/1538-4357/ac5fa6
