SN 2024aecx: Double-Peaked Light Curves and Rapid Evolution in a Nearby Type IIb Supernova
Qiang Xi, Ning-Chen Sun, David Aguado, Ismael P'erez-Fournon, Fr'ed'erick Poidevin, Junjie Jin, Yiming Mao, Zexi Niu, Beichuan Wang, Yu Zhang, Kuntal Misra, Divyanshu Janghel, Justyn R. Maund, Amit Kumar, Samaporn Tinyanont, Liang-Duan Liu, Yu-Hao Zhang, Bhavya Ailawadhi, Monalisa Dubey, Zhen Guo, Anshika Gupta, Min He, Dhruv Jain, Debalina Kar, Wenxiong Li, Joe D. Lyman, Haiyang Mu, Kumar Pranshu, Xinxiang Sun, Lingzhi Wang, Sarvesh Kumar Yadav, Yi-Han Zhao, Jie Zheng, Yinan Zhu, David L'opez Fern'andez-Nespral, Alicia L'opez Oramas, Yanan Wang, Klaas Wiersema, Jifeng Liu
Published: 2025/9/15
Abstract
SN 2024aecx is a nearby ($\sim$11 Mpc) Type IIb SN discovered within $\sim$1 d after explosion. In this paper we report high-cadence photometric and spectroscopic follow-up observations, conducted from as early as 0.27 d post discovery out to the nebular phase at 158.4 d. We analyze the environment of SN 2024aecx and derive a new distance, metallicity and host extinction. The light curve exhibits a hot and luminous shock-cooling peak at the first few days, followed by a main peak with very rapid post-maximum decline. The earliest spectra are blue and featureless, while from 2.3 d after discovery prominent P-Cygni profiles emerge. At nebular phase, the emission lines exhibit asymmetric and double-peaked profiles, indicating asphericity and/or early dust formation in the ejecta. We simulated the progenitor and explosion using a two-component model of shock cooling and radioactive $^{56}$Ni heating; our model favors an extended, low-mass H-rich envelope with$ M_{\mathrm{e}} = 0.08^{+0.02}_{-0.03}\, M_{\odot} $ and a low ejecta mass of $ M_{\mathrm{ej}} = 2.65^{+1.21}_{-0.73} \, M_{\odot}. $The comprehensive monitoring of SN 2024aecx, coupled with the detailed characterization of its local environment, establishes it as a benchmark event for probing the progenitors and explosion mechanisms of Type IIb SNe.