J/ApJ/959/132 KSP photometry of the Type Ia SN 2021aefx (Ni+, 2023)
Origin of high-velocity ejecta, excess emission, and redward color evolution in
the infant Type Ia supernova 2021aefx.
Ni Y.Qi, Moon D.-S., Drout M.R., Matzner C.D., Leong K.C.C., Kim S.C.,
Park H.S., Lee Y.
<Astrophys. J., 959, 132 (2023)>
=2023ApJ...959..132N 2023ApJ...959..132N
ADC_Keywords: Supernovae; Photometry, UBVRI
Keywords: Binary stars ; Supernovae ; Type Ia supernovae ; White dwarf stars ;
Transient sources ; Time domain astronomy
Abstract:
SN 2021aefx is a normal Type Ia supernova (SN) showing excess emission
and redward color evolution over the first ∼2days. We present analyses
of this SN using our high-cadence KMTNet multiband photometry,
spectroscopy, and publicly available data, including first
measurements of its explosion epoch (MJD59529.32±0.16) and onset of
power-law rise (tPL=MJD59529.85±0.55; often called first light)
associated with the main ejecta 56Ni distribution. The first KMTNet
detection of SN 2021aefx precedes tPL by ∼0.5hr, indicating presence
of additional power sources. Our peak-spectrum confirms its
intermediate Type Ia subclassification between core-normal and
broad-Line, and we estimate an ejecta mass of ∼1.34M☉. The
spectral evolution identifies material reaching >40000km/s (fastest
ever observed in Type Ia SNe) and at least two split-velocity ejecta
components expanding homologously:
(1) a normal-velocity (∼12400km/s) component consistent with typical
photospheric evolution of near-Chandrasekhar-mass ejecta; and
(2) a high-velocity (∼23500km/s) secondary component visible during
the first ∼3.6 days post-explosion, which locates the component within
the outer <16% of the ejecta mass.
Asymmetric subsonic explosion processes producing a nonspherical
secondary photosphere provide an explanation for the simultaneous
appearance of the two components, and may also explain the excess
emission via a slight 56Ni enrichment in the outer ∼0.5% of the ejecta
mass. Our 300 days post-peak nebular-phase spectrum advances
constraints against nondegenerate companions and further supports a
near-Chandrasekhar-mass explosion origin. Off-center ignited delayed-
detonations are likely responsible for the observed features of
SN2021aefx in some normal Type Ia SNe.
Description:
The discovery of SN 2021aefx was made by the Distance Less than 40Mpc
Survey (DLT40; Hosseinzadeh+ 2022, J/ApJ/933/L45) at an unfiltered
brightness of 17.24mag at 12h14m Universal Time (UT) on 2021-Nov-11
(MJD59529.343).
A subsequent spectrum obtained by Southern African Large Telescope
(SALT) at MJD59529.872 was H-poor with broad SiII absorption features
(Bostroem+ 2021TNSCR3888....1B 2021TNSCR3888....1B), identifying the source to be a
Type Ia SN.
We have conducted high-cadence, multicolor (BVI) monitoring
observations of the field containing the spiral galaxy host NGC 1566
using Korea Microlensing Telescope Network (KMTNet) as part of the
KMTNet Supernova Program (KSP; Moon+ 2016SPIE.9906E..4IM).
The KMTNet is composed of three 1.6m telescopes all equipped with a
wide-field CCD camera with 4deg2 field of view in Chile, South
Africa, and Australia, providing 24hr continuous sky coverage. Between
2021 November 1 and 2022 February 25, we obtained ∼1200 total images
of the field with 60s exposure time for individual frames reaching an
average 3σ detection limit of 21.3mag. On average, one set of
BVI-band images were obtained every ∼7hr.
We obtained spectra of SN 2021aefx from three different epochs
(2021-Nov-28.12, 2022-Jan-20.20 and 2022-Sep-27.37), including peak
and nebular phase, using the Gemini Multi-Object Spectrograph (GMOS)
on the 8m Gemini-South telescope. See Section 2.2.
Objects:
----------------------------------------------------------------------
RA (ICRS) DE Designation(s) (z)
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04 19 53.38 -54 56 53.2 SN 2021aefx = KSP-SN-2021v (z=0.005284)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 38 1056 KMTNet Supernova Program (KSP) photometry
of SN 2021aefx
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See also:
VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006)
J/ApJ/699/L139 : Spectral parameters of SNe Ia (Wang+, 2009)
J/AJ/143/126 : Spectroscopy of nearby Type Ia supernovae (Blondin+, 2012)
J/A+A/554/A27 : 2011fe spectrophotometric time series (Pereira+, 2013)
J/MNRAS/440/696 : HI absorption in nearby radio galaxies (Allison+, 2014)
J/ApJ/787/29 : UVOT phot. of Super-Chandrasekhar mass SNe Ia (Brown+, 2014)
J/MNRAS/451/1973 : Type Ia supernovae high-velocity features (Silverman+, 2015)
J/ApJ/826/56 : HST/WFC3 obs. of Cepheids in SN Ia host gal. (Riess+, 2016)
J/ApJ/869/56 : Updated calib. of the CSP-I SNe Ia sample (Burns+, 2018)
J/ApJ/881/22 : BVI phot. of TypeII SN KSP-SN-2016kf (Afsariardchi+, 2019)
J/ApJ/870/L1 : K2 obs. of type Ia supernova SN 2018oh (Dimitriadis+, 2019)
J/MNRAS/483/628 : SNIa properties using bolometric LCs (Scalzo+, 2019)
J/A+A/634/A37 : TURTLS Light curves of 56Ni distributions (Magee+, 2020)
J/ApJ/902/47 : ZTF early obs. of type Ia SNe. II. Rise time (Miller+, 2020)
J/ApJ/923/L8 : Follow-up phot. & sp. of SNIa 2020hvf (Jiang+, 2021)
J/ApJ/910/151 : KMTNet BVi photometry of SNIa KSP-OT-201509b (Moon+, 2021)
J/ApJ/933/L45 : LCs and spectra of type Ia SN 2021aefx (Hosseinzadeh+, 2022)
J/ApJ/925/L22 : KMTNet BVI LCs & spectroscopy of KSP-OT-201701a (Lee+, 2022)
J/ApJ/926/L25 : New LBT/MODS spectra of type Ia SN 2011fe (Tucker+, 2022)
J/A+A/678/A170 : Effective collision strengths for Ni III (Blondin+, 2023)
J/ApJ/946/7 : BVI light curves and sp. of Type Ia SN 2018aoz (Ni+, 2023)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 F11.5 d MJD [59529.8/59635.1] Modified Julian Date
13- 13 A1 --- Band [BVi] Observation band (1)
15- 20 F6.3 mag mag [11.87/16.85] Apparent magnitude in Band (1)
22- 26 F5.3 mag emagDet [0.006/0.07] The 1σ detection uncertainty
28- 32 F5.3 mag emagTot [0.01/0.08] The 1σ total uncertainty (2)
34- 38 F5.1 --- S/N [16.2/195.3] Signal to Noise
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Note (1): The BV-band magnitudes are in the Vega system, while the i-band
magnitudes are in the AB system (see Section 2.1 text).
Note (2): Includes the detection S/N, the photometric calibration error, and
the S-correction error (see Section 2.1 text).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 29-Jan-2026