Observational diversity of bright long-lived Type II supernovae

¹ Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
² Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
³ Aalto University Department of Electronics and Nanoengineering, P.O. BOX 15500, FI-00076 AALTO, Finland
⁴ Cosmic Dawn Center (DAWN), Copenhagen, Denmark
⁵ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 København N, Denmark
⁶ Finnish Centre for Astronomy with ESO (FINCA), University of Turku, FI-20014 Turku, Finland
⁷ Centro de Astronomía (CITEVA), Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile
⁸ School of Sciences, European University Cyprus, Diogenes Street, Engomi, 1516 Nicosia, Cyprus
⁹ Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan
¹⁰ The Oskar Klein Centre, Department of Astronomy, AlbaNova, SE-106 91 Stockholm, Sweden
¹¹ European Southern Observatory, Alonso de Córdova 3107, Casilla 19, Santiago, Chile
¹² Millennium Institute of Astrophysics MAS, Nuncio Monsenor Sotero Sanz 100, Off. 104, Providencia, Santiago, Chile
¹³ Cardiff Hub for Astrophysics Research and Technology, School of Physics & Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK
¹⁴ Graduate Institute of Astronomy, National Central University, 300 Jhongda Road, 32001 Jhongli, Taiwan
¹⁵ Instituto de Astrofísica de La Plata, CONICET, B1900FWA La Plata, Argentina
¹⁶ Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N B1900FWA, La Plata, Argentina
¹⁷ School of Physics, University College Dublin, LMI Main Building, Beech Hill Road, Dublin 4, D04 P7W1, Ireland
¹⁸ Astrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, UK
¹⁹ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
²⁰ Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC, 08860 Castelldefels (Barcelona), Spain
²¹ Institute of Space Sciences (ICE, CSIC), Campus UAB, Carrer de Can Magrans, s/n, E-08193 Barcelona, Spain
²² Instituto de Alta Investigación, Universidad de Tarapacá, Casilla 7D, Arica, Chile
²³ School of Physics, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
²⁴ Instituto de Ciencias Exactas y Naturales (ICEN), Universidad Arturo Prat, Iquique, Tarapacá, Chile
²⁵ Dipartimento di Fisica “Ettore Pancini”, Università di Napoli Federico II, Via Cinthia 9, 80126 Naples, Italy
²⁶ INAF – Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 Naples, Italy
²⁷ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (LC), Italy
²⁸ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, I-35122 Padova, Italy
²⁹ School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
³⁰ Center for Astrophysics and Cosmology, University of Nova Gorica, Vipavska 11c, 5270 Ajdovščina, Slovenia

^⋆ Corresponding author: takashi.nagao@utu.fi

Received: 1 April 2025
Accepted: 2 June 2025

Abstract

Context. In various types of supernovae (SNe), strong interaction between the SN ejecta and circumstellar material (CSM) has been reported. This raises questions about their progenitors and mass-loss processes shortly before the explosion. Recently, the bright long-lived Type II SN 2021irp was proposed to be a standard Type II SN interacting with disk-like CSM. The observational properties suggest that the progenitor was a massive star (∼8−18 M_⊙) in a binary system and underwent a mass-ejection process due to the binary interaction just before the explosion. Similar scenarios, i.e., a Type II SN interacting with a CSM disk, have also been invoked to explain some Type IIn SNe.

Aims. Here, we study the diversity of the observational properties of bright long-lived Type II (21irp-like) SNe. We analyze the diversity of their CSM properties, in order to understand their progenitors and mass-loss mechanisms and their relations with the other types of interacting SNe.

Methods. We performed photometry, spectroscopy, and/or polarimetry for four 21irp-like SNe. Based on these observations as well as published data of SN 2021irp itself and well-observed bright and long-lived type II SNe including SNe 2010jl, 2015da, and 2017hcc, we discuss their CSM characteristics.

Results. This sample of SNe shows luminous and long-lived photometric evolution, with some variations in the photometric evolution (from ∼−17 to ∼−20 absolute mag in the r/o band even at ∼200 days after the explosion). They show photospheric spectra characterized mainly by Balmer lines for several hundreds of days, with some variations in the shapes of the lines. They show high polarization with slight variations in the polarization degrees (∼1−3% at the brightness peak) with rapid declines with time (from ∼3−6% before the peak to ∼1% at ∼200 days after the peak). The general observational properties are consistent with the disk-CSM-interaction scenario, i.e., typical Type II SNe interacting with disk-like CSM. At the same time, the variation in the observational properties suggest diversity in the CSM mass and the opening angle of the CSM disk. These variations in the CSM properties are likely to be be related to the binary parameters of the progenitor systems and/or the properties of the progenitor and companion stars.