WFST Supernovae in the First Year: II. SN 2024aedt: Systematical Study of a Transitional Type Ia Supernova

TL;DR

SN 2024aedt is a well-sampled transitional Type Ia supernova that lies between normal and 91bg-like populations in both light-curve decline and color evolution. By combining WFST photometry, multi-epoch spectroscopy, SALT2/SNooPy light-curve fitting, MOSFiT physical modeling, and host-galaxy SED analysis, the study derives $M_B = -18.49 \pm 0.03$ mag, $\Delta m_{15}(B) = 1.53 \pm 0.36$ mag, $M(^{56}$Ni$) = 0.414 \pm 0.042\,M_{\odot}$, and $M_{ej} = 0.548 \pm 0.108\,M_{\odot}$, placing it in the 86G-like transitional subclass. Spectral diagnostics reveal early-time blue-end diversity that becomes more homogeneous with time, underscoring the diagnostic value of early observations. Model comparisons indicate that both delayed-detonation (DDT) and double-detonation (DDet) scenarios can reasonably reproduce the data, with pseudo-bolometric fits favoring DDet with a thin He shell, though interpretation is sensitive to viewing angle and model limitations. The work demonstrates the power of prompt, high-cadence surveys like WFST to illuminate the progenitor and explosion physics of SNe Ia and aims to build a larger transitional SN Ia sample for robust constraint of these channels.

Abstract

We present comprehensive photometric and spectroscopic observations of a transitional type Ia SN 2024aedt, discovered by the 2.5-meter Wide Field Survey Telescope (WFST) within one day of the explosion. Its light curve is characterized by a peak absolute magnitude of $M_B = -18.49 \pm 0.03$ mag and a decline rate of $Δm_{15}(B) = 1.53 \pm 0.36$ mag, placing the object on the $Δm_{15}(B)$--$M_B$ diagram in the transition region between normal and subluminous SNe Ia. Furthermore, the early-color evolution and host galaxy environment of SN 2024aedt underscore its transitional nature, sharing properties with both normal and 91bg-like SNe Ia. Light-curve modeling with MOSFiT yields a synthesized $^{56}\mathrm{Ni}$ mass of $0.414 \pm 0.042\,M_{\odot}$ and a total ejecta mass of $0.548 \pm 0.108\,M_{\odot}$. A comparison with theoretical models suggests that the evolutionary trend can be broadly explained by both delayed-detonation (DDT) and double-detonation (DDet) scenarios while possible early-excess emissions predicted by DDet cannot be identified given the limited detections soon after the SN explosion. Although the overall spectral evolution of SN 2024aedt is similar to that of other transitional SNe Ia, the spectroscopic comparison reveals diversity in the early-phase blue-end features, which becomes more homogeneous at later phases. The result indicates the importance of early-time observations in understanding the origin of SN Ia diversity.

Figures (20)

• Figure 1: A three-color composite image of SN 2024aedt, observed by WFST on 2024-12-25. The image is constructed from $u$ (blue), $g$ (green), and $r$ (red) filter data. The position of the supernova is marked by the red circle. A $30^{\prime\prime}$ scale bar is shown in the bottom-left corner.
• Figure 2: Multi-band light curves of SN 2024aedt. The photometry for each band is color-coded as shown in the legend. Triangles denote 5$\sigma$ upper limits.
• Figure 3: The $u-g$ and $g-r$ color evolution of SN 2024aedt, calculated from nightly-binned WFST photometry.
• Figure 4: Spectra of SN 2024aedt from multiple epochs and instruments. For display purposes, an arbitrary offset has been applied to the flux of each spectrum. The original data are shown as faint lines, while the solid lines are smoothed versions using a Savitzky-Golay filter Savitzky1964. Shaded regions mark the locations of telluric absorption.
• Figure 5: Power-law fit to the early $g$-band light curve. The fitting procedure and results are described in Section \ref{['subsec:exp']}.