Yongzhi Cai, A. Pastorello, Keiichi Maeda, Jiewei Zhao, Z.-Y. Wang, Zhongmin Peng, A. Reguitti, L. Tartaglia, Alex Filippenko, Pan Yu, G. Valerin, Brijesh Kumar, Z. Wang, M. Fraser, J. P. Anderson, S. Benetti, S. Bose, T. G. Brink, E. Cappellaro, T. -W. Chen, Xinxing Chen, N. Elias-Rosa, Ali Esamdin, A. Gal-Yam, Maider González-Bañuelos, M. Gromadzki, C. P. Gutiérrez, C. Inserra, Abdusamatjan Iskandar, T. Kangas, E. Kankare, T. Kravtsov, H. Kuncarayakti, Leping Li, C.-X. Liu, X.-K. Liu, P. Lundqvist, K. Matilainen, S. Mattila, S. Moran, T.E Müller-Bravo, T. Nagao, T. Petrushevska, G. Pignata, I. Salmaso, S. J. Smartt, J. Sollerman, Shubham Srivastav, M. Stritzinger, Letian Wang, S. -Y. Yan, You Yang, Y.-P. Yang, W. Zheng, Xingzhu Zou, Liyang Chen, Xuan Du, Q. Fang, A. Fiore, Fabio Ragosta, Shuai Zha, J. -J. Zhang, X. -W. Liu, J. M. Bai, Bo Wang, X. -F. Wang
We present a photometric and spectroscopic analyses of the Type Ibn supernova (SN) 2024acyl. It rises to an absolute magnitude peak of M o = −17.58 ± 0.15 mag in 10.6 days, and displays a rapid linear post-peak light-curve decline in all bands (e.g. γ 0 − 60 ( V ) = 0.097 ± 0.002 mag day −1 ), similar to most SNe Ibn. The optical pseudobolometric light curve peaks at (3.5 ± 0.8)×10 42 erg s −1 , with a total radiated energy of (5.0 ± 0.4)×10 48 erg. The spectra are dominated by a blue continuum at early stages, with narrow P-Cygni He I lines and flash-ionisation emission lines of C III , N III , and He II . The P-Cygni He I features gradually evolve and become emission-dominated in late-time spectra. The H α line is detected throughout the entire spectral evolution, which indicates that the circumstellar material (CSM) is helium-rich with some residual amount of hydrogen. Our multi-band light-curve modelling yields estimates of the ejecta mass of M ej = 0.49 +0.11 −0.09 M ⊙ with a kinetic energy of E k = 0.06 +0.01 −0.01 × 10 51 erg, and a 56 Ni mass of M Ni = 0.018 M ⊙ . The inferred CSM properties are characterised by a mass of M CSM = 0.51 +0.05 −0.04 M ⊙ , an inner radius of R 0 =17.8 +3.6 −3.0 AU, and a density of ρ CSM = (8.3 +2.7 −1.2 ) × 10 −12 g cn −3 . The multi-epoch spectra are well reproduced by the CMFGEN/ he4p0 model, corresponding to a He-ZAMS mass of 4 M ⊙ (H-ZAMS mass 18.11 M ⊙ , pre-SN mass 3.16 M ⊙ ). These findings are consistent with a scenario of an SN powered by ejecta-CSM interaction originating from a low-mass helium star that evolved within an interacting binary system where the CSM with some residual hydrogen may originate from the mass-transfer process. We also discuss an extreme scenario involving the possible merger of a helium white dwarf. In addition, a channel of core-collapse explosion of a late-type Wolf-Rayet (WR) star with hydrogen, or a transitional star between an Of and a WR type (e.g. an Ofpe/WN9 star) with fallback accretion cannot be entirely ruled out.