Direct evidence of two-component ejecta in supernova 2016gkg from nebular spectroscopy

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] $\lambda \lambda 6300,6364$ and [Ca II] $\lambda \lambda 7292,7324$. Other notable, albeit weaker, emission lines include Mg I] $\lambda 4571$, [Fe II] $\lambda 7155$, O I $\lambda 7774$, Ca II triplet, and a broad, boxy feature at the location of H$\alpha$. 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]$\lambda 6300,6364$ line: a broad component (width $\sim 2000$ km s${}^{-1}$), and a pair of narrow blue and red components (width $\sim 300$ 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 multi-dimensional explosion modeling of SNe.

arXiv comment20 pages, 11 figures, accepted to ApJ

References in corpus (69)

• Starburst99: Synthesis Models for Galaxies with Active Star Formation
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Cosmic-Ray Rejection by Laplacian Edge Detection
• WISeREP - An Interactive Supernova Data Repository
• Automated data reduction workflows for astronomy
• A comprehensive classification of galaxies in the SDSS: How to tell true from fake AGN?
• The HIPASS Catalogue - I. Data Presentation
• The O3N2 and N2 abundance indicators revisited: improved calibrations based on CALIFA and Te-based literature data
• A giant outburst two years before the core-collapse of a massive star
• An Open Catalog for Supernova Data
• ZAP -- Enhanced PCA Sky Subtraction for Integral Field Spectroscopy
• Bolometric light curves and explosion parameters of 38 stripped-envelope core-collapse supernovae
• Non-spherical Core Collapse Supernovae I. Neutrino-Driven Convection, Rayleigh-Taylor Instabilities, and the Formation and Propagation of Metal Clumps
• Three-dimensional neutrino-driven supernovae: Neutron star kicks, spins, and asymmetric ejection of nucleosynthesis products
• Evolution, Explosion and Nucleosynthesis of Core Collapse Supernovae
• Asymmetries in core-collapse supernovae from maps of radioactive ${}^{44}$Ti in CassiopeiaA
• Nucleosynthesis in Type II Supernovae
• Three-Dimensional Simulations of Core-Collapse Supernovae: From Shock Revival to Shock Breakout
• Bipolar Supernova Explosions: Nucleosynthesis & Implication on Abundances in Extremely Metal-Poor Stars
• Detailed Analysis of Early to Late-Time Spectra of Supernova 1993J
• Asphericity in Supernova Explosions from Late-Time Spectroscopy
• An Asymmetric, Energetic Type Ic Supernova Viewed Off-Axis, and a Link to Gamma-Ray Bursts
• A non-spherical core in the explosion of supernova SN 2004dj
• Photometric and spectroscopic evolution of the type IIP supernova SN 2004et
• A Spectroscopic Analysis of the Energetic Type Ic `Hypernova' SN 1997ef
• The Carnegie Supernova Project I: analysis of stripped-envelope supernova light curves
• Nebular emission-line profiles of Type Ib/c Supernovae - probing the ejecta asphericity
• The nebular spectra of SN 2012aw and constraints on stellar nucleosynthesis from oxygen emission lines
• Photometric and Spectroscopic Properties of Type II-P Supernovae
• Nucleosynthesis and Clump Formation in a Core Collapse Supernova
• A Two-Component Model for the Light Curves of Hypernovae
• The nebular spectra of the hypernova SN 1998bw and evidence for asymmetry
• Late-time spectral line formation in Type IIb supernovae, with application to SN 1993J, SN 2008ax, and SN 2011dh
• Quantitative Spectroscopy of Photospheric-Phase Type II Supernovae
• Signatures of a jet cocoon in early spectra of a supernova associated with a $\gamma$-ray burst
• SN 2009jf: a slow-evolving stripped-envelope core-collapse supernova
• Double-peaked Oxygen Lines Are not Rare in Nebular Spectra of Core-Collapse Supernovae
• Characterising the environments of supernovae with MUSE
• Direct Confirmation of the Asymmetry of the Cas A Supernova with Light Echoes
• A surge of light at the birth of a supernova
• SN 1998bw at late phases
• Doublets and Double Peaks: Late-Time [O I] 6300, 6364 Line Profiles of Stripped-Envelope, Core-Collapse Supernovae
• The Type IIb SN 2011dh - Two years of observations and modelling of the lightcurves
• The AMUSING++ Nearby Galaxy Compilation: I. Full Sample Characterization and Galactic--Scale Outflows Selection
• The Berkeley Sample of Stripped-Envelope Supernovae
• Optical Emission from Aspherical Supernovae and the Hypernova SN 1998bw
• Dust and the type II-Plateau supernova 2004dj
• The impact of fallback on the compact remnants and chemical yields of core-collapse supernovae
• Constraints on core-collapse supernova progenitors from explosion site integral field spectroscopy
• Nebular phase observations of the type-Ib supernova iPTF13bvn favour a binary progenitor
• Constraints on the Progenitor of SN 2016gkg From Its Shock-Cooling Light Curve
• The progenitor and early evolution of the Type IIb SN 2016gkg
• Direct evidence for a supernova interacting with a large amount of hydrogen-free circumstellar material
• SN2010jp (PTF10aaxi): A Jet-Driven Type II Supernova
• On the Progenitor of the Type IIb Supernova 2016gkg
• A mildly relativistic radio jet from the otherwise normal Type Ic Supernova 2007gr
• Supernova Nebular Spectroscopy Suggests a Hybrid Envelope-Stripping Mechanism for Massive Stars
• Simulations of light curves and spectra for superluminous Type Ic supernovae powered by magnetars
• SN 2017gmr: An energetic Type II-P supernova with asymmetries
• Radiative-transfer models for explosions from rotating and non-rotating single WC stars. Implications for SN1998bw and LGRB/SNe
• Optical studies of SN 2009jf: A type Ib supernova with an extremely slow decline and aspherical signature
• SN 2017dio: a type-Ic supernova exploding in a hydrogen-rich circumstellar medium
• After the Fall: Late-Time Spectroscopy of Type IIP Supernovae
• Evidence for a pulsar wind nebula in the Type Ib-peculiar supernova SN 2012au
• The aspherical explosion of the Type IIP SN 2017gmr
• Indications of a Si-rich bilateral jet of ejecta in the Vela SNR observed with XMM-Newton
• Numerically Modeling the First Peak of the Type IIb SN 2016gkg
• Type Ib SN 1999dn as an example of the thoroughly mixed ejecta of Ib supernovae
• Strongly Bipolar Inner Ejecta of the Normal Type IIP Supernova ASASSN-16at

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