SN 2024iss: Double-Peaked Light Curves and Implications for a Yellow Supergiant Progenitor

Abstract

We report the multi-band photometric observations of the Type IIb supernova (SN) 2024iss with ultra-violet (UV), optical, and near-infrared (NIR) wavelengths starting one day after the explosion. The UV and optical light curves show the first peak two days after the explosion date. Following a first peak, a secondary maximum is observed in the optical and NIR bands, similar to SNe IIb with double-peaked light curves. The quasi-bolometric light curve shows the fast decay until a week after the explosion. From the analysis of the bolometric light curve, the ejecta mass and kinetic energy are estimated to be $M_{ej}=2.8\pm 0.6M_{\odot }$ and $E_{kin}=9.4\pm 4.1\times 10^{50}$ erg. The mass of the radioactive ${}^{56}$Ni is estimated to be $M{(}^{56}Ni)=0.2M_{\odot }$. Fitting a black-body function to the spectral energy distribution reveals that the photospheric temperature exhibits a rapid exponential decline during the first week after the explosion. An analytic model describing the cooling emission after shock breakout provides a reasonable explanation for the observed temperature evolution. From these ejecta parameters, we calculated the progenitor radius to be $R_{pro}=50-340$~$R_{\odot }$. We conclude that these explosion properties are consistent with a core-collapse explosion from a yellow supergiant (YSG) progenitor.

6 pages, 5 figures, accepted for publication on Publications of the Astronomical Society of Japan on 2025-Mar-06, line break correction