SN 2020wnt: a slow-evolving carbon-rich superluminous supernova with no O II lines and a bumpy light curve

We present the analysis of SN 2020wnt, an unusual hydrogen-poor superluminous supernova (SLSN-I), at a redshift of 0.032. The light curves of SN 2020wnt are characterized by an early bump lasting ∼5 d, followed by a bright main peak. The SN reaches a peak absolute magnitude of Mmaxr=−20.52±0.03 mag at ∼77.5 d from explosion. This magnitude is at the lower end of the luminosity distribution of SLSNe-I, but the rise-time is one of the longest reported to date. Unlike other SLSNe-I, the spectra of SN 2020wnt do not show O II, but strong lines of C II and Si II are detected. Spectroscopically, SN 2020wnt resembles the Type Ic SN 2007gr, but its evolution is significantly slower. Comparing the bolometric light curve to hydrodynamical models, we find that SN 2020wnt luminosity can be explained by radioactive powering. The progenitor of SN 2020wnt is likely a massive and extended star with a pre-SN mass of 80 M⊙ and a pre-SN radius of 15 R⊙ that experiences a very energetic explosion of 45 × 1051 erg, producing 4 M⊙ of 56Ni. In this framework, the first peak results from a post-shock cooling phase for an extended progenitor, and the luminous main peak is due to a large nickel production. These characteristics are compatible with the pair-instability SN scenario. We note, however, that a significant contribution of interaction with circumstellar material cannot be ruled out.
MB and MO acknowledge support from UNRN PI2020 40B885 and grant PICT-2020-SERIEA-01141 and PIP 112-202001-10034. AR acknowledges support from ANID BECAS/DOCTORADO NACIONAL 21202412. TMR acknowledges the financial support of the Finnish Academy of Science and Letters. NER acknowledges partial support from MIUR, PRIN 2017 (grant 20179ZF5KS), from the Spanish MICINN grant PID2019-108709GB-I00 and FEDER funds, and from the program Unidad de Excelencia María de Maeztu CEX2020-001058-M. MF is supported by a Royal Society – Science Foundation Ireland University Research Fellowship. SM acknowledges support from the Magnus Ehrnrooth Foundation and the Vilho, Yrjö and Kalle Väisälä Foundation. MS was a visiting astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract 80HQTR19D0030 with the National Aeronautics and Space Administration. XW is supported by the National Science Foundation of China (NSFC grants 12033003 and 11633002), the Scholar Program of Beijing Academy of Science and Technology (DZ:BS202002), and the Tencent Xplorer Prize. JZ is supported by the NSFC (grants 12173082, 11773067), by the Youth Innovation Promotion Association of the CAS (grant 2018081), and by the Ten Thousand Talents Program of Yunnan for Top-notch Young Talents. Funding for the LJT has been provided by Chinese Academy of Sciences and the People’s Government of Yunnan Province. The LJT is jointly operated and administrated by Yunnan Observatories and Center for Astronomical Mega-Science, CAS. This work is supported by the National Natural Science Foundation of China (NSFC grants 12033003, 11633002, 11325313, and 11761141001), the National Program on Key Research and Development Project (grant no. 2016YFA0400803). This work is partially supported by China Manned Spaced Project (CMS-CSST-2021-A12). This work is funded by China Postdoctoral Science Foundation (grant no. 2021M691821).