Supernova 2020wnt: An Atypical Superluminous Supernova with a Hidden Central Engine
Kilpatrick, Charles D.; Foley, Ryan J.; Jones, David O.; Pan, Yen-Chen; Tinyanont, Samaporn; Sollerman, Jesper; Perley, Daniel A.; Taggart, Kirsty; De, Kishalay; Fremling, Christoffer; Kasliwal, Mansi M.; Lunnan, Ragnhild; Schulze, Steve; Dong, Dillon Z.; Dimitriadis, Georgios; Jha, Saurabh W.; Rojas-Bravo, César; Siebert, Matthew R.; Yan, Lin; Ravi, Vikram; Davis, Kyle W.; Sfaradi, Itai; Woosley, Stan E.; Chen, Ting-Wan; Gagliano, Alexander; Clever, Karoli E.; Smith, Carli; Ashall, Chris; Miao, Hao-Yu; Alarcon, Vanessa; Angulo, Rodrigo; Crawford, Payton; Couch, Cirilla; Dandu, Srujan; Dhara, Atirath; Johnson, Jessica; Lai, Zhisen
United States, Thailand, Sweden, Ireland, Taiwan, United Kingdom, Israel
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) × 1043 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.