Supernova 2020wnt: An Atypical Superluminous Supernova with a Hidden Central Engine

Tinyanont, Samaporn and Woosley, Stan E. and Taggart, Kirsty and Foley, Ryan J. and Yan, Lin and Lunnan, Ragnhild and Davis, Kyle W. and Kilpatrick, Charles D. and Siebert, Matthew R. and Schulze, Steve and Ashall, Chris and Chen, Ting-Wan and De, Kishalay and Dimitriadis, Georgios and Dong, Dillon Z. and Fremling, Christoffer and Gagliano, Alexander and Jha, Saurabh W. and Jones, David O. and Kasliwal, Mansi M. and Miao, Hao-Yu and Pan, Yen-Chen and Perley, Daniel A. and Ravi, Vikram and Rojas-Bravo, Cesar and Sfaradi, Itai and Sollerman, Jesper and Alarcon, Vanessa and Angulo, Rodrigo and Clever, Karoli E. and Crawford, Payton and Couch, Cirilla and Dandu, Srujan and Dhara, Atirath and Johnson, Jessica and Lai, Zhisen and Smith, Carli (2023) Supernova 2020wnt: An Atypical Superluminous Supernova with a Hidden Central Engine. The Astrophysical Journal, 951 (1): 34. ISSN 0004-637X

Abstract

We present observations of a peculiar hydrogen- and helium-poor stripped-envelope (SE) supernova (SN) 2020wnt, primarily in the optical and near-infrared (near-IR). Its peak absolute bolometric magnitude of −20.9 mag (L bol, peak = (6.8 ± 0.3) × 10 43 erg s −1) and a rise time of 69 days are reminiscent of hydrogen-poor superluminous SNe (SLSNe I), luminous transients potentially powered by spinning-down magnetars. Before the main peak, there is a brief peak lasting <10 days post explosion, likely caused by interaction with circumstellar medium (CSM) ejected ∼years before the SN explosion. The optical spectra near peak lack a hot continuum and O ii absorptions, which are signs of heating from a central engine; they quantitatively resemble those of radioactivity-powered hydrogen/helium-poor Type Ic SESNe. At ∼1 yr after peak, nebular spectra reveal a blue pseudo-continuum and narrow O i recombination lines associated with magnetar heating. Radio observations rule out strong CSM interactions as the dominant energy source at +266 days post peak. Near-IR observations at +200-300 days reveal carbon monoxide and dust formation, which causes a dramatic optical light-curve dip. Pair-instability explosion models predict slow light curve and spectral features incompatible with observations. SN 2020wnt is best explained as a magnetar-powered core-collapse explosion of a 28 M ⊙ pre-SN star. The explosion kinetic energy is significantly larger than the magnetar energy at peak, effectively concealing the magnetar-heated inner ejecta until well after peak. SN 2020wnt falls into a continuum between normal SNe Ic and SLSNe I, and demonstrates that optical spectra at peak alone cannot rule out the presence of a central engine.