What question did this study set out to answer?

This research aims to analyze the photometric and spectroscopic features of the Type Ibn supernova SN 2024acyl.

February 6, 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

Key Points

This research aims to analyze the photometric and spectroscopic features of the Type Ibn supernova SN 2024acyl.
Conducted photometric analysis to measure the absolute magnitude peak and light-curve decline.
Performed spectroscopic analysis to identify emission lines and continuum features.
Utilized multi-band light-curve modeling to estimate ejecta mass and kinetic energy.
Examined CSM properties based on spectral evolution.
SN 2024acyl peaks at absolute magnitude of -17.58 in 10.6 days with a linear decline.
The total radiated energy estimated at 5.0 x 10^51 erg.
Ejecta mass estimated at 0.49 M⊙ with kinetic energy of 0.06 x 10^51 erg.
Circumstellar material characterized by a mass of 0.51 M⊙ and helium-rich composition.

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 mathrm mag, -1), similar to most SNe Ibn. The optical pseudobolometric light curve peaks at (3. 5 erg s 10^ 42 -1, with a total radiated energy of (5. 0 erg. The spectra are dominated by a blue continuum at early stages, with narrow P-Cygni ̋ei lines and flash-ionisation emission lines of C 10^ 48 iii, N iii, and He ii. The P-Cygni ̋ei features gradually evolve and become emission-dominated in late-time spectra. The ̋a 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, with a kinetic energy of E_ k = 0. 06^ +0. 01 _ -0. 01 10^ 51, , and a erg 56 Ni mass of M_ Ni = 0. 018, The inferred CSM properties are characterised by a mass of M_ CSM = 0. 51^ +0. 05 _ -0. 04 an inner radius of R₀=17. 8^ +3. 6 _ -3. 0 AU, and a density of ρ_ CSM = (8. 3_ -1. 2 ^ +2. 7), -12 -3. The multi-epoch spectra are well reproduced by the CMFGEN/ 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. he4p0

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