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

TL;DR

SN 2020wnt is a peculiar superluminous supernova with signs of a hidden central engine, likely a magnetar, which influences its light curve and spectra, bridging the gap between normal SNe Ic and SLSNe I.

Contribution

This study provides detailed observations and analysis of SN 2020wnt, revealing it as a magnetar-powered core-collapse supernova with unique spectral and light curve features that challenge existing classifications.

Findings

SN 2020wnt shows a brief pre-peak peak likely caused by CSM interaction.

Spectral features near peak resemble radioactivity-powered SNe Ic, not typical SLSNe.

Nebular spectra reveal magnetar heating effects at late times.

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 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 OII absorptions, which are signs of heating from a central engine; they quantitatively resemble those of radioactivity-powered H/He-poor Type Ic SESNe. At ~1 year after peak, nebular spectra reveal a blue pseudo-continuum and narrow OI 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 day 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 Msun 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.