Analyzing the Largest Spectroscopic Dataset of Hydrogen-Poor Super-Luminous Supernovae

TL;DR

This study systematically analyzes the spectral features of hydrogen-poor super-luminous supernovae (SLSNe Ic) and compares them with other supernova types to understand their origins and connection with gamma-ray bursts.

Contribution

It provides a comprehensive spectral comparison of 32 SLSNe Ic, 21 SNe Ic-bl, and 17 SNe Ic, developing new tools for spectral analysis and testing models of supernova power sources.

Findings

SLSNe Ic and SNe Ic-bl have similar spectral feature widths and velocities.

SLSNe Ic exhibit higher absorption velocities than SNe Ic by about 7,000 km/s.

The spectral properties challenge the interaction model and are inconsistent with a simple magnetar model.

Abstract

Super-luminous supernovae (SLSNe) are tremendously luminous explosions whose power sources and progenitors are highly debated. Broad-lined SNe Ic (SNe Ic-bl) are the only type of SNe that are connected with long-duration gamma ray bursts (GRBs). Studying the spectral similarity and difference between the populations of hydrogen-poor SLSNe (SLSNe Ic) and of hydrogen-poor stripped-envelope core-collapse SNe, in particular SNe Ic and SNe Ic-bl, can provide crucial observations to test predictions of theories based on various power source models and progenitor models. In this paper, we collected all of the published optical spectra of 32 SLSNe Ic, 21 SNe Ic-bl, as well as 17 SNe Ic, quantified their spectral features, constructed average spectra, and compared them in a systematic way using new tools we have developed. We find that SLSNe Ic and SNe Ic-bl, including those connected with GRBs, have comparable widths for their spectral features and average absorption velocities at all phases. Thus, our findings strengthen the connection between SLSNe Ic and GRBs. In particular, SLSNe Ic have average \FeII absorption velocities of $-15,000 +/- 2,600$ \kms~at 10 days after peak, which are higher than those of SNe Ic by $\sim7,000$ \kms~on average. SLSNe Ic also have significantly broader \FeII lines than SNe Ic. Moreover, we find that such high absorption and width velocities of SLSNe Ic may be hard to explain by the interaction model, and none of 13 SLSNe Ic with measured absorption velocities spanning over 10 days has a convincing flat velocity-evolution, which is inconsistent with the magnetar model in one dimension. Lastly, we compare SN 2011kl, the first SN connected with an ultra-long GRB, with the mean spectrum of SLSNe Ic and of SNe Ic-bl.