Work

Coupled Shock Cooling and Radioactive Heating in SN 2024aecx: An Extended Envelope and Rapid Optical Decline

Year: 2026

Type: article

Abstract: SN 2024aecx is a nearby, rapidly evolving stripped-envelope supernova with a prominent double-peaked ultraviolet–optical light curve. We model its multiband evolution with an extended version of TransFit , in which the early shock-cooling emission and the subsequent radioactive heating are treated within a single time-dependent radiative diffusion calculation. To describe the stratified ejecta required by the early shock-cooling emission, we adopt compact inner ejecta connected to a dilute extended outer envelope and fit the outer density slope directly from the early light curve. The model reproduces the short-lived first peak, the rise to the radioactive main peak, and the overall multiband evolution. We infer an effective outer radius of R 0 = 264.1 4 − 87.50 + 139.86 R ⊙ , an ejecta mass of M ej = 3.0 1 − 0.47 + 0.74 M ⊙ , a nickel mass of M Ni = 0.1 6 − 0.01 + 0.02 M ⊙ , and a steep outer density slope of n out = 14.6 8 − 0.51 + 0.24 . The steep outer profile favors a low-mass extended envelope, while the inferred ejecta mass is consistent with the rapid evolution of the main peak. However, a control model with standard γ -ray leakage fades too slowly after maximum. We therefore introduce an effective optical-output factor to quantify the additional late-time suppression of the ultraviolet–optical luminosity. These results support the shock-cooling plus radioactive-heating interpretation of SN 2024aecx, but show that its rapid optical decline requires physics beyond the simplest radioactive-diffusion prescription.

Source: The Astrophysical Journal

DOI: 10.3847/1538-4357/aea6a9