SN 2021aaev: A hydrogen-rich superluminous supernova with early flash and long-lived circumstellar interaction in an unusual host environment

Hu, Yang, Lunnan, Ragnhild, Pessi, PriscilaJ., Saldana-Lopez, Alberto, Jerkstrand, Anders, Sollerman, Jesper, Schulze, Steve and Inserra, Cosimo ORCID: https://orcid.org/0000-0002-3968-4409 2026. SN 2021aaev: A hydrogen-rich superluminous supernova with early flash and long-lived circumstellar interaction in an unusual host environment. The Astrophysical Journal 999 (2) , 176. 10.3847/1538-4357/ae374c

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Abstract

We present photometric and spectroscopic observations of SN 2021aaev, a hydrogen-rich, superluminous supernova with persistent (at least ∼100 days) narrow Balmer lines (SLSN-IIn) at redshift z = 0.1557. SN 2021aaev rose over 28.1 ± 1.0 rest-frame days after explosion, reaching a peak absolute magnitude of −21.46 ± 0.01 in the ATLAS o band. The prepeak spectra resemble those of typical Type IIn SNe with flash-ionization features arising from the interaction with a dense, confined circumstellar medium (CSM), albeit the flash timescale is longer than usual (>20 days). Postpeak, the narrow emission lines evolve slowly, and the absence of ejecta features indicates strong deceleration by the CSM. The total radiated energy (about 1.41 × 1051 erg) is possibly explained by a low-mass (1–2 M⊙) ejecta ploughing into a massive (9–19 M⊙), extended (outer radius >1 × 1016 cm) H-rich CSM, or alternatively by magnetar-powered models. Interestingly, the host environment consists of a spiral galaxy with a red substructure in the southeastern part, and the SN’s exact location coincides with this quiescent red region (star formation rate =0.02−0.02+0.13M⊙ yr−1). Given the atypical environment and the obscuring effect of the massive CSM, a thermonuclear (Type Ia-CSM) origin cannot be ruled out. Altogether, SN 2021aaev is a compelling case to study the diversity of SLSN-IIn features and their host environments.

Item Type:	Article
Date Type:	Published Online
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	License information from Publisher: LICENSE 1: URL: https://creativecommons.org/licenses/by/4.0/, Type: cc-by
Publisher:	American Astronomical Society
ISSN:	0004-637X
Date of First Compliant Deposit:	9 March 2026
Date of Acceptance:	7 January 2026
Last Modified:	09 Mar 2026 11:16
URI:	https://orca.cardiff.ac.uk/id/eprint/185588

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