Origin of High-velocity Ejecta, Excess Emission, and Redward Color Evolution in the Infant Type Ia Supernova 2021aefx
Bibliographic record
Abstract
Abstract SN 2021aefx is a normal Type Ia supernova (SN) showing excess emission and redward color evolution over the first ∼ 2 days. 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 (MJD 59529.32 ± 0.16) and onset of power-law rise (t PL = MJD 59529.85 ± 0.55; often called first light) associated with the main ejecta 56Ni distribution. The first KMTNet detection of SN 2021aefx precedes t PL by ∼ 0.5 hr, 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 ∼ 1.34 M ⊙. The spectral evolution identifies material reaching >40,000 km s−1 (fastest ever observed in Type Ia SNe) and at least two split-velocity ejecta components expanding homologously: (1) a normal-velocity (∼ 12,400 km s−1) component consistent with typical photospheric evolution of near-Chandrasekhar-mass ejecta; and (2) a high-velocity (∼ 23,500 km s−1) 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 SN 2021aefx in some normal Type Ia SNe.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".