In:
The Astrophysical Journal, American Astronomical Society, Vol. 902, No. 2 ( 2020-10-01), p. 139-
Abstract:
Spectral observations of the type-IIb supernova (SN) 2016gkg at 300–800 days are reported. The spectra show nebular characteristics, revealing emission from the progenitor star’s metal-rich core and providing clues to the kinematics and physical conditions of the explosion. The nebular spectra are dominated by emission lines of [O i ] λλ 6300, 6364 and [Ca ii ] λλ 7292, 7324. Other notable, albeit weaker, emission lines include Mg I] λ 4571, [Fe ii ] λ 7155, O I λ 7774, Ca II triplet, and a broad, boxy feature at the location of H α . Unlike in other stripped-envelope SNe, the [O i ] doublet is clearly resolved due to the presence of strong narrow components. The doublet shows an unprecedented emission line profile consisting of at least three components for each [O i ] λ 6300, 6364 line: a broad component (width ∼2000 km s −1 ), and a pair of narrow blue and red components (width ∼300 km s −1 ) mirrored against the rest velocity. The narrow component appears also in other lines, and is conspicuous in [O i ]. This indicates the presence of multiple distinct kinematic components of material at low and high velocities. The low-velocity components are likely to be produced by a dense, slow-moving emitting region near the center, while the broad components are emitted over a larger volume. These observations suggest an asymmetric explosion, supporting the idea of two-component ejecta that influence the resulting late-time spectra and light curves. SN 2016gkg thus presents striking evidence for significant asymmetry in a standard-energy SN explosion. The presence of material at low velocity, which is not predicted in 1D simulations, emphasizes the importance of multidimensional explosion modeling of SNe.
Type of Medium:
Online Resource
ISSN:
0004-637X
,
1538-4357
DOI:
10.3847/1538-4357/abb4e7
Language:
Unknown
Publisher:
American Astronomical Society
Publication Date:
2020
detail.hit.zdb_id:
2207648-7
detail.hit.zdb_id:
1473835-1
SSG:
16,12
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