Direct Evidence of Two-component Ejecta in Supernova 2016gkg from Nebular Spectroscopy*

Kuncarayakti, H.; Folatelli, G.; Maeda, Keiichi; Jerkstrand, A.; Anderson, J. P.; Aoki, Kentaro; Bersten, Melina C.; Ferrari, L.; Galbany, L.; García, Federico; Gutiérrez, C. P.; Hattori, Takashi; Kawabata, Koji S.; Kravtsov, Timo; Lyman, J. D.; Mattila, S.; Olivares, E. F.; Sánchez, S. F.; Dyk, Schuyler D. Van

doi:10.3847/1538-4357/abb4e7

Cited by 9 publications

(11 citation statements)

References 86 publications

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“…Taking the endpoint luminosity as an indicator for the initial mass of the progenitor star, this would place SN 2016gkg at 10 2019), we model this phase of the light curve assuming that SN 2016gkg initially produced 0.085 M of 56 Ni and assuming its light curve is powered primarily by radioactive decay from 250-652 days post-explosion. This assumption is supported by the overall light curve shape at this phase as well as the lack of strong spectroscopic features due to interaction with CSM at <500 days (Figure 3 and Kuncarayakti et al 2020).…”

Section: Hst Photometry Of Sn 2016gkg and Its Progenitor Starmentioning

confidence: 60%

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Updated Photometry of the Yellow Supergiant Progenitor and Late-time Observations of the Type IIb Supernova 2016gkg

Kilpatrick,

Coulter,

Foley

et al. 2021

Preprint

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We present Hubble Space Telescope (HST) observations of the type IIb supernova (SN) 2016gkg at 652, 1698, and 1795 days from explosion with the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). Comparing to pre-explosion imaging from 2001 obtained with the Wide Field Planetary Camera 2, we demonstrate that SN 2016gkg is now fainter than its candidate counterpart in the latest WFC3 imaging, implying that the counterpart has disappeared and confirming that it was the SN progenitor star. We show the latest light curve and Keck spectroscopy of SN 2016gkg, which implies that SN 2016gkg is declining more slowly than the expected rate for 56 Co decay during its nebular phase. We find that this emission is too luminous to be powered by other radioisotopes, thus we infer that SN 2016gkg is entering a new phase in its evolution where it is powered primarily by interaction with circumstellar matter. Finally, we re-analyze the progenitor star spectral energy distribution and late-time limits in the context of binary evolution models and including emission from a potential companion star and find that all companion stars would be fainter than our limiting magnitudes.

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Section: Hst Photometry Of Sn 2016gkg and Its Progenitor Starmentioning

confidence: 60%

“…We highlight lines of [Mg I] λ4571, [O I] λλ6300, 6364, Hα, and [Ca II] λλ7292, 7324. For comparison, we show the latest Gemini-S/GMOS spectrum fromKuncarayakti et al (2020), which shows that Hα emission is enhanced as the SN evolves.…”

mentioning

confidence: 99%

Updated Photometry of the Yellow Supergiant Progenitor and Late-time Observations of the Type IIb Supernova 2016gkg

Kilpatrick,

Coulter,

Foley

et al. 2021

Preprint

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“…There is indeed evidence from the observed skewness of emission line profiles that even standard-energy SN Ibc ejecta are asymmetric (Taubenberger et al 2009;Milisavljevic et al 2010). Alternate power sources and asymmetry will also allow for a description of exceptional late time properties, for example with the hybrid line profile morphology observed in SN 2016gkg (Kuncarayakti et al 2020). Our study suggests that metal yields are just one component influencing the nebular-phase properties of SNe Ibc, and that a proper characterization of these events requires a global and physically-consistent modeling of their complex ejecta structure.…”

Section: Discussionmentioning

confidence: 94%

“…The properties of core-collapse SNe at nebular times are complex, but offer the potential to constrain some important characteristics of the progenitor star and its explosion (see, for example, Fransson & Chevalier 1989;Jerkstrand 2017). These characteristics include the yields from intermediate mass elements (e.g., O or Ca) and iron group elements (for example the initial abundance of 56 Ni, or more rarely stable Ni; Jerkstrand et al 2015b), the geometry of the inner ejecta (Mazzali et al 2001;Maeda et al 2006Maeda et al , 2008Modjaz et al 2008;Taubenberger et al 2009;Milisavljevic et al 2010), the formation of dust and molecules (Kotak et al 2005(Kotak et al , 2006Rho et al 2018Rho et al , 2021, or the late-time source of power for the ejecta (see for example the peculiar nebular phase spectral properties of SN 2016gkg; Kuncarayakti et al 2020). By combining the analysis of both photospheric-phase and nebular-phase properties, one can build a more consistent picture of core-collapse SNe, which can provide important constraints for massive star evolution and explosion.…”

Section: Introductionmentioning

confidence: 99%

Nebular phase properties of supernova Ibc from He-star explosions

Hillier

Sukhbold

Woosley

et al. 2021

A&A

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Following our recent work on Type II supernovae (SNe), we present a set of 1D nonlocal thermodynamic equilibrium radiative transfer calculations for nebular-phase Type Ibc SNe starting from state-of-the-art explosion models with detailed nucleosynthesis. Our grid of progenitor models is derived from He stars that were subsequently evolved under the influence of wind mass loss. These He stars, which most likely form through binary mass exchange, synthesize less oxygen than their single-star counterparts with the same zero-age main sequence (ZAMS) mass. This reduction is greater in He-star models evolved with an enhanced mass loss rate. We obtain a wide range of spectral properties at 200 d. In models from He stars with an initial mass > 6 M⊙, the [O I] λλ 6300, 6364 is of a comparable or greater strength than [Ca II] λλ 7291, 7323 – the strength of [O I] λλ 6300, 6364 increases with the He-star initial mass. In contrast, models from lower mass He stars exhibit a weak [O I] λλ 6300, 6364, strong [Ca II] λλ 7291, 7323, and also strong N II lines and Fe II emission below 5500 Å. The ejecta density, which is modulated by the ejecta mass, the explosion energy, and clumping, has a critical impact on gas ionization, line cooling, and spectral properties. We note that Fe II dominates the emission below 5500 Å and is stronger at earlier nebular epochs. It ebbs as the SN ages, while the fractional flux in [O I] λλ 6300, 6364 and [Ca II] λλ 7291, 7323 increases with a similar rate as the ejecta recombine. Although the results depend on the adopted wind mass loss rate and pre-SN mass, we find that He-stars of 6–8 M⊙ initially (ZAMS mass of 23–28 M⊙) match the properties of standard SNe Ibc adequately. This finding agrees with the offset in progenitor masses inferred from the environments of SNe Ibc relative to SNe II. Our results for less massive He stars are more perplexing since the predicted spectra are not seen in nature. They may be missed by current surveys or associated with Type Ibn SNe in which interaction power dominates over decay power.

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“…We further investigate the nature of AT 2016jbu by looking at its local environment in Integral Field Unit (IFU) data. (Galbany et al 2016;Kuncarayakti et al 2020). We downloaded the pre-calibrated data cubes from the ESO archive and present our data analysis for the environment around AT 2016jbu in Fig.…”

Section: Muse -Ing On the Local Environmentmentioning

confidence: 99%

Progenitor, environment, and modelling of the interacting transient, AT 2016jbu (Gaia16cfr)

Brennan,

Fraser,

Johansson

et al. 2021

Preprint

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In the second of two papers on the peculiar interacting transient AT 2016jbu, we present the bolometric lightcurve, identification and analysis of the progenitor candidate, as well as preliminary modelling to help elucidate the nature of this event. We identify the progenitor candidate for AT 2016jbu in quiescence, and find it to be consistent with a ∼ 20 M yellow hypergiant surrounded by a dusty circumstellar shell. We see evidence for significant photometric variability in the progenitor, as well as strong Hα emission consistent with pre-existing circumstellar material. The age of the resolved stellar population surrounding AT 2016jbu, as well as integral-field unit spectra of the region support a progenitor age of >16 Myr, again consistent with a progenitor mass of ∼20 M . Through a joint analysis of the velocity evolution of AT 2016jbu, and the photospheric radius inferred from the bolometric lightcurve, we find that the transient is consistent with two successive outbursts or explosions. The first outburst ejected a shell of material with velocity 650 km s −1 , while the second more energetic event ejected material at 4500 km s −1 . Whether the latter is the core-collapse of the progenitor remains uncertain, as the required ejecta mass is relatively low (few tenths of M ). We also place a restrictive upper limit on the ejected 56 Ni mass of <0.016 M . Using the BPASS code, we explore a wide range of possible progenitor systems, and find that the majority of these are in binaries, some of which are undergoing mass transfer or common envelope evolution immediately prior to explosion. Finally, we use the SNEC code to demonstrate that the low-energy explosion of some of these systems together with sufficient CSM can reproduce the overall morphology of the lightcurve of AT 2016jbu.

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Direct Evidence of Two-component Ejecta in Supernova 2016gkg from Nebular Spectroscopy*

Cited by 9 publications

References 86 publications

Updated Photometry of the Yellow Supergiant Progenitor and Late-time Observations of the Type IIb Supernova 2016gkg

Updated Photometry of the Yellow Supergiant Progenitor and Late-time Observations of the Type IIb Supernova 2016gkg

Nebular phase properties of supernova Ibc from He-star explosions

Progenitor, environment, and modelling of the interacting transient, AT 2016jbu (Gaia16cfr)

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