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Massive stars exploding in a He-rich circumstellar medium: XII. SN 2024acyl: A fast, linearly declining Type Ibn supernova with early flash-ionisation features
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A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
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Astronomy and Astrophysics, Volume 707
Abstract
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.
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Cai, Y Z, Pastorello, A, Maeda, K, Zhao, J W, Wang, Z Y, Peng, Z H, Reguitti, A, Tartaglia, L, Filippenko, A V, Pan, Y, Valerin, G, Kumar, B, Wang, Z, Fraser, M, Anderson, J P, Benetti, S, Bose, S, Brink, T G, Cappellaro, E, Chen, T W, Chen, X L, Elias-Rosa, N, Esamdin, A, Gal-Yam, A, González-Bañuelos, M, Gromadzki, M, Gutiérrez, C P, Inserra, C, Iskandar, A, Kangas, T, Kankare, E, Kravtsov, T, Kuncarayakti, H, Li, L P, Liu, C X, Liu, X K, Lundqvist, P, Matilainen, K, Mattila, S, Moran, S, Müller-Bravo, T E, Nagao, T, Petrushevska, T, Pignata, G, Salmaso, I, Smartt, S J, Sollerman, J, Srivastav, S, Stritzinger, M D, Wang, L T, Yan, S Y, Yang, Y, Yang, Y P, Zheng, W, Zou, X Z, Chen, L Y, Du, X L, Fang, Q L, Fiore, A, Ragosta, F, Zha, S, Zhang, J J, Liu, X W, Bai, J M, Wang, B & Wang, X F 2026, 'Massive stars exploding in a He-rich circumstellar medium: XII. SN 2024acyl: A fast, linearly declining Type Ibn supernova with early flash-ionisation features', Astronomy and Astrophysics, vol. 707, A157. https://doi.org/10.1051/0004-6361/202558014