Massive stars exploding in a He-rich circumstellar medium

XI. Diverse evolution of five Ibn SNe 2020nxt, 2020taz, 2021bbv, 2023utc, and 2024aej

¹ School of Physics and Astronomy, Beijing Normal University, Beijing 100875, China
² Department of Physics, Faculty of Arts and Sciences, Beijing Normal University, Zhuhai 519087, China
³ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁴ Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, China
⁵ International Centre of Supernovae, Yunnan Key Laboratory, Kunming 650216, China
⁶ Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650216, China
⁷ School of Physics, O’Brien Centre for Science North, University College Dublin, Belfield, Dublin 4, Ireland
⁸ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
⁹ Department of Astronomy, Xiamen University, Xiamen, Fujian 361005, China
¹⁰ Department of Physics, Tsinghua University, Beijing 100084, China
¹¹ INAF – Osservatorio Astronomico d’Abruzzo, Via M. Maggini snc, 64100 Teramo, Italy
¹² Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117-5575, USA
¹³ Department of Physics, University of California, Santa Barbara, CA 93106-9530, USA
¹⁴ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, E-08193 Barcelona, Spain
¹⁵ Institut für Theoretische Physik, Goethe Universität, Max-von-Laue-Str. 1, 60438 Frankfurt am Main, Germany
¹⁶ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138-1516, USA
¹⁷ The NSF AI Institute for Artificial Intelligence and Fundamental Interactions, USA
¹⁸ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
¹⁹ Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
²⁰ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, SE-10691 Stockholm, Sweden
²¹ Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
²² Max-Planck-Institut für Astrophysik, Karl-Schwarzschild Str. 1, D-85748 Garching, Germany
²³ School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
²⁴ College of Science, Chongqing University of Posts and Telecommunications, Chongqing 400065, China
²⁵ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast BT7 1NN, UK
²⁶ Astrophysics sub-Department, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
²⁷ Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
²⁸ Adler Planetarium, 1300 S. DuSable Lake Shore Drive, Chicago, IL 60605, USA
²⁹ Department of Physics, Stellenbosch University, Matieland 7602, South Africa
³⁰ National Institute for Theoretical and Computational Sciences (NITheCS), South Africa
³¹ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
³² Institute for Astronomy, University of Hawai’i, 2680 Woodlawn Drive, Honolulu HI, 96822, USA
³³ Institut d’Estudis Espacials de Catalunya (IEEC), 08860 Castelldefels (Barcelona), Spain
³⁴ Finnish Centre for Astronomy with ESO (FINCA), Quantum, Vesilinnantie 5, University of Turku, FI-20014 Turku, Finland
³⁵ School of Physics and Electrical Engineering, Liupanshui Normal University, Liupanshui, Guizhou 553004, China
³⁶ Cosmic Dawn Center (DAWN), Denmark
³⁷ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 København N, Denmark
³⁸ School of Physics and Electronic Information, Jiangsu Second Normal University, Nanjing, Jiangsu 211200, China
³⁹ Institute for Frontier in Astronomy and Astrophysics, Beijing Normal University, Beijing 102206, China
⁴⁰ Advanced Institute of Natural Sciences, Beijing Normal University, Zhuhai 519087, China

^⋆ Corresponding authors: caiyongzhi@ynao.ac.cn; linwl@xmu.edu.cn; zhuxj@bnu.edu.cn

Received: 26 March 2025
Accepted: 16 June 2025

Abstract

We present the photometric and spectroscopic analysis of five Type Ibn supernovae (SNe): SN 2020nxt, SN 2020taz, SN 2021bbv, SN 2023utc, and SN 2024aej. These events share key observational features and belong to a family of objects similar to the prototypical Type Ibn SN 2006jc. The SNe exhibit rise times of approximately 10 days and peak absolute magnitudes ranging from −16.5 to −19 mag. Notably, SN 2023utc is the faintest Type Ibn SN discovered to date, with an exceptionally low r-band absolute magnitude of −16.4 mag. The pseudo-bolometric light curves peak at (1 − 10)×10⁴² erg s⁻¹, with total radiated energies on the order of (1 − 10)×10⁴⁸ erg. Spectroscopically, these SNe display a relatively slow spectral evolution. The early spectra are characterised by a hot blue continuum and prominent He I emission lines. The early spectra also show blackbody temperatures exceeding 10 000 K, with a subsequent decline in temperature during later phases. Narrow He I lines, which are indicative of unshocked circumstellar material (CSM), show velocities of approximately 1000 km s⁻¹. The spectra suggest that the progenitors of these SNe underwent significant mass loss prior to the explosion, resulting in a He-rich CSM. Our light curve modelling yielded estimates for the ejecta mass (M_ej) in the range 1 − 3 M_⊙ with kinetic energies (E_Kin) of (0.1 − 1)×10⁵⁰ erg. The inferred CSM mass ranges from 0.2 to 1 M_⊙. These findings are consistent with expectations for core collapse events arising from relatively massive envelope-stripped progenitors.