Characterization of Type Ibn Supernovae

¹ DARK, Niels Bohr Institute, University of Copenhagen, Jagtvej 155A, 2200 Copenhagen, Denmark
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³ Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
⁴ OzGrav, School of Physics, The University of Melbourne, VIC 3010, Parkville, Australia
⁵ The NSF AI Institute for Artificial Intelligence and Fundamental Interactions, USA
⁶ Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁷ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
⁸ Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W. Green St., IL 61801, USA
⁹ Center for Astrophysical Surveys, National Center for Supercomputing Applications, Urbana, IL 61801, USA
¹⁰ NSF-Simons SkAI Institute, 875 N. Michigan Ave., Chicago, IL 60611, USA
¹¹ Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD 21218, USA
¹² Astrophysics Research Center of the Open University (ARCO), The Open University of Israel, Ra’anana, 4353701 Israel
¹³ Department of Natural Sciences, The Open University of Israel, Ra’anana 4353701, Israel
¹⁴ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
¹⁵ Hubble Fellow, Department of Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
¹⁶ Institute for Astronomy, University of Hawaii, 640 N.‘Aohoku Pl., Hilo, HI 96720, USA
¹⁷ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA
¹⁸ Department of Physics, Fisk University, 1000 17th Avenue N. Nashville, TN 37208, USA
¹⁹ Department of Physics, Lancaster University, Lancaster, LA1 4YB, UK
²⁰ Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 106 91 Stockholm, Sweden
²¹ INAF, Osservatorio Astronomico di Capodimonte, salita Moiariello 16, 80131 Naples, Italy
²² Observatories of the Carnegie Institute for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA
²³ Space Telescope Science Institute, Baltimore, MD 21218, USA
²⁴ National Astronomical Research Institute of Thailand, 260 Moo 4, Donkaew, Maerim, Chiang Mai 50180, Thailand

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Received: 15 June 2025
Accepted: 17 February 2026

Abstract

Context. Type Ibn supernovae (SNe) are characterized by narrow helium (He I) lines from photons produced by the unshocked circumstellar material (CSM). About 80 SNe Ibn have been discovered to date and only a handful of them have extensive observational records. Thus, many open questions remain regarding the progenitor system and the origin of CSM.

Aims. Here, we investigate potential correlations between the spectral features of the prominent He I λ5876 Å line and the optical and X-ray light curve properties of Type Ibn SNe (SNe Ibn).

Methods. We compiled the largest sample of 61 SNe Ibn to date, of which 24 SNe have photometric and spectroscopic data available from the Young Supernova Experiment and 37 SNe benefit from archival datasets. We fit 24 SNe Ibn with sufficient photometric coverage (B to z bands) using semi-analytical models from MOSFiT.

Results. We demonstrate that the light curves of SNe Ibn are more diverse than previous analyses suggest, with absolute r-band peak magnitudes (r_max) of −19.4 ± 0.6 mag, along with rise (from −10 days to peak, γ₋₁₀) and decay rates (from peak to +10 days; γ₊₁₀) of −0.08 ± 0.06 and 0.08 ± 0.03 mag/day, respectively. We find that the majority of SNe Ibn in the subsample are consistent with a low-energy explosion (< 10⁵¹ erg) of a star with a compact envelope surrounded by ~0.1 M_⊙ of helium-rich CSM. The inferred ejecta masses are small (M_ej ~ 1 M_⊙) and expand with a velocity of ~5000 km/s. Our spectroscopic analysis shows that the mean velocity of the narrow component of the He I lines, associated with the CSM, peaks at ~1100 km/s.

Conclusions. The mean CSM and ejecta masses inferred for a subsample of SNe Ibn indicate that their progenitors are not massive (~10 M_⊙) single stars at the moment of explosion; rather, they are likely to be binary systems. This finding is in agreement with detections of potential companion stars of SNe Ibn progenitors and inferred CSM properties from stellar evolution models.