Transitional events in the spectrophotometric regime between stripped envelope and superluminous supernovae

TL;DR

This paper investigates four supernovae that exhibit characteristics of both stripped-envelope and superluminous supernovae, revealing transitional objects with unique spectroscopic and photometric properties that challenge existing classification boundaries.

Contribution

It provides detailed analysis of four transitional supernovae, highlighting their unique photometric and spectroscopic features that bridge the gap between SE-SNe and SLSNe.

Findings

Transitional supernovae show long-lived, variable luminosity near the SLSN threshold.

Spectroscopically, these objects resemble SE-SNe with lower line velocities.

They represent rare cases that challenge the traditional supernova classification scheme.

Abstract

The division between stripped-envelope supernovae (SE-SNe) and superluminous supernovae (SLSNe) is not well defined in either photometric or spectroscopic space. While a sharp luminosity threshold has been suggested, there remains an increasing number of transitional objects that reach this threshold without the spectroscopic signatures common to SLSNe. In this work we present data and analysis on four SNe transitional between SE-SNe and SLSNe; the He-poor SNe 2019dwa and 2019cri, and the He-rich SNe 2019hge and 2019unb. Each object displays long-lived and variable photometric evolution with luminosities around the SLSN threshold of $M_r < -19.8$ mag. Spectroscopically however, these objects are similar to SE-SNe, with line velocities lower than either SE-SNe and SLSNe, and thus represent an interesting case of rare transitional events.