2026-05-28T23:45:06Zivo://CDS.VizieR/J/A+A/707/A1572026-03-03T19:24:01ZJ.A_AIVOASN 2024acyl light curvesWe present a photometric and spectroscopic analysis of the Type Ibn supernova (SN) 2024acyl. It rises to an absolute magnitude peak of M_o=-17.58+/-0.15mag in 10.6 days, and displays a rapid linear post-peak light-curve decline in all bands (e.g., gamma_0-60(V)_=0.097+/-0.002mag/d), similar to most SNe Ibn. The optical pseudobolometric light curve peaks at (3.5+/-0.8)x10^42^erg/s, with a total radiated energy of (5.0+/-0.4)x10^48^erg. The spectra are dominated by a blue continuum at early stages, with narrow P-Cygni HeI lines and flash-ionisation emission lines of CIII, NIII, and HeII. The P-Cygni HeI features gradually evolve and become emission-dominated in late-time spectra. The H-alpha 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 multiband light-curve modelling yields estimates of the ejecta mass of M_ej_=0.49^+0.11^_-0.09_M_{sun}_, with a kinetic energy of E_k_=0.06^+0.01^_-0.01_x10^51^erg, and a ^56^Ni mass of M_Ni_=0.018M_{sun}_. The inferred CSM properties are characterised by a mass of M_CSM_= 0.51 (+0.05/-0.04) M_sun, an inner radius of R_0_=17.8^+3.6^_-3.0_AU, and a density rho_CSM_=(8.3^+2.7^_-1.2_)x10^-12^g/cm^3^. The multi-epoch spectra are well reproduced by the CMFGEN/he4p0 model, corresponding to a He-ZAMS mass of 4M_{sun}_ (H-ZAMS mass 18.11M_{sun}_, pre-SN mass 3.16M_{sun}_). 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 (CC) explosion of a late-type Wolf-Rayet (WR) star with hydrogen (WNH), 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.supernovaephotometryvisible-astronomyultraviolet-astronomystellar-astronomyobservational-astronomyhttps://dc.g-vo.org/rr/q/lp/custom/CDS.VizieR/J/A+A/707/A157https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/707/A1572026A&A...707A.157Chttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/707/A157Cai 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.Gonzalez-Banuelos M.Gromadzki M.Gutierrez 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.Mueller-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.CDS2026https://cds.unistra.fr/vizier-org/licences_vizier.htmlCDS support team <cds-question@unistra.fr>DatasetAstroObjectsastronomy