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

Abstract

We present the analysis of SN 2020wnt, an unusual hydrogen-poor super-luminous supernova (SLSN-I), at a redshift of 0.032. The light curves of SN 2020wnt are characterised by an early bump lasting ∼5 days, followed by a bright main peak. The SN reaches a peak absolute magnitude of M$_{r}^{max}=-20.52\pm 0.03$ mag at ∼77.5 days 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.

Premaximum Spectroscopic Diversity of Hydrogen-poor Superluminous Supernovae

“…It is present in the premaximum of 26 examined and can be characterized with a temperature between 12,000 and 15,000 K (Inserra 2019). In accordance with this finding, the T phot values of Type 15bn SLSNe-I were found to be smaller or equal to 12,000 K, while Type W objects were modeled applying larger temperatures, in some cases even exceeding 15,000 K. Gutiérrez et al (2022) studied the A lower (T phot = 13,000 K) and a higher (T phot = 17,000 K) model is plotted as well with green and blue colors, respectively. The three models share the same global and local parameters with the exception of the photospheric temperature.…”

“…This discovery allowed Nicholl et al (2016b) to suggest that such bumps may be usual/omnipresent features in SLSNe-I; however, this theory was refuted by Angus et al (2019), who carried out a detailed analysis of SLSNe-I from the Dark Energy Survey and found that only three SLSNe-I showed early bumps in their sample of 14 objects. Later on, PFT12dam (Vreeswijk et al 2017), and potentially SN 2018bsz (e.g., Anderson et al 2018;Chen et al 2021;Gutiérrez et al 2022;Pursiainen et al 2022) and SN 2018hti (Lin et al 2020;Fiore et al 2022) were revealed to show early LC undulations. Gutiérrez et al (2022) examined this topic in detail and found that some SLSNe-I that show smooth LC in their early phase can be characterized by slow photometric evolution (e.g., SN 2007bi, Gal-Yam et al 2009Young et al 2010;LSQ14an, Inserra et al 2017;SN 2015bn, Nicholl et al 2016a, 2016bSN 2017gci, Fiore et al 2021 in their sample).…”

“…Later on, PFT12dam (Vreeswijk et al 2017), and potentially SN 2018bsz (e.g., Anderson et al 2018;Chen et al 2021;Gutiérrez et al 2022;Pursiainen et al 2022) and SN 2018hti (Lin et al 2020;Fiore et al 2022) were revealed to show early LC undulations. Gutiérrez et al (2022) examined this topic in detail and found that some SLSNe-I that show smooth LC in their early phase can be characterized by slow photometric evolution (e.g., SN 2007bi, Gal-Yam et al 2009Young et al 2010;LSQ14an, Inserra et al 2017;SN 2015bn, Nicholl et al 2016a, 2016bSN 2017gci, Fiore et al 2021 in their sample).…”

“…It was shown previously in the literature that some SLSNe-I show undulations in their premaximum LCs, often referred as "early bumps." On the contrary, normal Type Ic SNe tend to evolve smoothly both before and after the moment of the maximum (e.g., Nicholl 2021; Gutiérrez et al 2022), which can be another difference between normal SNe-Ic and SLSNe-I. At first, Leloudas et al (2012) identified an early bump in the LC of SN 2006oz, which was followed by additional identifications of prepeak undulations in the light, for example, in the cases of LSQ14bdq (Nicholl et al 2015b) and DES14X3taz (Smith et al 2016).…”

Near-infrared and Optical Observations of Type Ic SN 2021krf: Luminous Late-time Emission and Dust Formation

“…Including the Sc II features improved the fitting between 4000 and 6000 Å, even though Sc is not commonly identified in SN Ic spectra. Recently, Gutiérrez et al (2022) also found Sc II in spectra of SN 2020wnt, a peculiar hydrogen-poor Type I SLSN. Since SLSN-I spectra are somewhat similar to those of SNe Ic, the presence of Sc II is not unexpected.…”