Origin of high-velocity ejecta and early red excess emission in the infant Type Ia supernova 2021aefx

Abstract

SN~2021aefx is a normal Type Ia Supernova (SN) with red excess emission over the first $\sim$ 2 days. We present detailed analysis of this SN using our high-cadence KMTNet multi-band photometry, spectroscopy, and publicly available data. We provide the first measurements of its epochs of explosion (MJD 59529.32 $\pm$ 0.16) as well as ``first light'' (MJD 59529.85 $\pm$ 0.55) associated with the main ejecta ${}^{56}\mathrm{Ni}$ distribution. This places our first detection of SN 2021aefx at $\sim -$0.5 hours since ``first light'', indicating the presence of additional power sources. Our peak-spectrum confirms its Type Ia sub-classification as intermediate between Core-Normal and Broad-Line, and we estimate the ejecta mass to be $\sim$ 1.34 $M_{\odot }$. The pre-peak spectral evolution identifies fast-expanding material reaching $>$ 40,000 km s${}^{-1}$ (the fastest ever observed in Type Ia SNe) and at least two distinct homologously-expanding ejecta components: (1) a normal-velocity (12,400 km s${}^{-1}$) component consistent with the typical photospheric evolution of Chandrasekhar-mass ejecta; and (2) a high-velocity (23,500 km s${}^{-1}$) component visible during the first $\sim$ 3.6 days post-explosion, which locates the component within the outer $<$ 16\% of the ejecta mass. Asymmetric, subsonic explosion processes producing a non-spherical photosphere provide an explanation for the simultaneous presence of the two components, as well as the red excess emission via a slight ${}^{56}\mathrm{Ni}$ enrichment in the outer $\sim$ 0.5\% of the ejecta mass. Our spectrum from 300 days post-peak advances the constraint against non-degenerate companions and further supports a near-Chandrasekhar-mass explosion origin. Off-center ignited delayed-detonations of Chandrasekhar-mass white dwarfs may be responsible for the observed features of SN 2021aefx in some normal Type Ia SNe.

Published in ApJ. 31 pages, 14 figures, 4 tables

References in corpus (40)

• A Common Explosion Mechanism for Type Ia Supernovae
• Confined Dense Circumstellar Material Surrounding a Regular Type II Supernova: The Unique Flash-Spectroscopy Event of SN 2013fs
• Improved Distances to Type Ia Supernovae with Two Spectroscopic Subclasses
• The Spectroscopic Diversity of Type Ia Supernovae
• The Carnegie Supernova Project: Intrinsic Colors of Type Ia Supernovae
• Signatures of a jet cocoon in early spectra of a supernova associated with a $\gamma$-ray burst
• Early Blue Excess from the Type Ia Supernova 2017cbv and Implications for Its Progenitor
• A hybrid type Ia supernova with an early flash triggered by helium-shell detonation
• The Outermost Ejecta of Type Ia Supernovae
• Double Detonations with Thin, Modestly Enriched Helium Layers Can Make Normal Type Ia Supernovae
• A search for HI absorption in nearby radio galaxies using HIPASS
• Non-Local Thermodynamic Equilibrium Radiative Transfer Simulations of Sub-Chandrasekhar-Mass White Dwarf Detonations
• Multi-Dimensional Parameter Study of Double Detonation Type Ia Supernovae Originating from Thin-Helium-Shell White Dwarfs
• H-$\alpha$ emission in the nebular spectrum of the Type Ia supernova ASASSN-18tb
• Determining the ${}^{56}$Ni distribution of type Ia supernovae from observations within days of explosion
• Discovery of the Fastest Early Optical Emission from Overluminous SN Ia 2020hvf: A Thermonuclear Explosion within a Dense Circumstellar Environment
• Dwarf Galaxy Discoveries from the KMTNet Supernova Program I. The NGC 2784 Galaxy Group
• WALLABY Early Science - III. An HI Study of the Spiral Galaxy NGC 1566
• Ultraviolet Observations of Super-Chandrasekhar Mass Type Ia Supernova Candidates with Swift UVOT
• Carnegie Supernova Project: The First Homogeneous Sample of "Super-Chandrasekhar Mass"/2003fg-like Type Ia Supernova
• Constraining Type Ia supernova explosions and early flux excesses with the Zwicky Transient Factory
• Carnegie Supernova Project-II: A new method to photometrically identify sub-types of extreme Type Ia Supernovae
• A JWST Near- and Mid-Infrared Nebular Spectrum of the Type Ia Supernova 2021aefx
• A Speed Bump: SN 2021aefx Shows that Doppler Shift Alone can Explain Early-Excess Blue Flux in Some Type Ia Supernovae
• Smoothed Particle Hydrodynamics simulations of the core-degenerate scenario for Type Ia supernovae
• Infant-phase reddening by surface Fe-peak elements in a normal Type Ia Supernova
• Revealing progenitors of type Ia supernovae from their light curves and spectra
• SN 2021zny: an early flux excess combined with late-time oxygen emission suggests a double white dwarf merger event
• Observations of the Very Young Type Ia Supernova 2019np with Early-excess Emission
• JWST Low-Resolution MIRI Spectral Observations of SN~2021aefx: High-density Burning in a Type Ia Supernova
• Spectral signatures of H-rich material stripped from a non-degenerate companion by a Type Ia supernova
• Can Helium-detonation Model Explain the Observed Diversity of Type Ia Supernovae?
• Nebular spectra from Type Ia supernova explosion models compared to JWST observations of SN 2021aefx
• Nebular H$\alpha$ Limits for Fast Declining Type Ia Supernovae
• A Rapid Ionization Change in the Nebular-Phase Spectra of the Type Ia SN 2011fe
• The origin and evolution of the normal Type Ia SN 2018aoz with infant-phase reddening and excess emission
• Improving Bayesian posterior correlation analysis on Type Ia supernova luminosity evolution
• Rapidly-Declining Hostless Type Ia Supernova KSP-OT-201509b from the KMTNet Supernova Program: Transitional Nature and Constraint on ${}^{56}$Ni Distribution and Progenitor Type
• Discovery of a Short-Period and Unusually Helium-Deficient Dwarf Nova KSP-OT-201701a by the KMTNet Supernova Program
• Direct Analysis of the Broad-Line SN 2019ein: Connection with the Core-Normal SN 2011fe

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