J/ApJ/959/132ivo://CDS.VizieR/J/ApJ/959/132CDSNi Y.QiMoon D.-S.Drout M.R.Matzner C.D.Leong K.C.C.Kim S.C.,Park H.S.Lee Y.2026-02-25T14:46:41Z2026-02-25T15:43:10ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsupernovaeinfrared-photometryvisible-astronomybroad-band-photometrySN 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 (t_PL_=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_{sun}_. 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.2023ApJ...959..132Nhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/959/132CatalogResearchIsServedByTAP VizieR generic servicerelated-toVII/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 ^56^Ni 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)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/959/132https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/959/132http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/959/132https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/959/132https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/959/132http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/959/132GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticalInfrareddefaultJ/ApJ/959/132/table1KMTNet Supernova Program (KSP) photometry of SN 2021aefxrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJD[59529.8/59635.1] Modified Julian Datedtime.epochdoubleBand[BVi] Observation band (1)meta.code;instr.filtercharmag[11.87/16.85] Apparent magnitude in Band (1)magphot.magfloatemagDet[0.006/0.07] The 1{sigma} detection uncertaintymagstat.error;phot.magfloatemagTot[0.01/0.08] The 1{sigma} total uncertainty (2)magstat.error;phot.magfloatS/N[16.2/195.3] Signal to Noisestat.snrfloat