LSQ13ddu: A rapidly-evolving stripped-envelope supernova with early circumstellar interaction signatures

TL;DR

This paper reports on the discovery and analysis of LSQ13ddu, a rapidly evolving supernova with early circumstellar interaction signatures, unusual spectral features, and a light curve explained by CSM interaction and radioactive decay.

Contribution

It provides detailed observations of a unique supernova with early circumstellar interaction and characterizes its spectral and light curve properties, highlighting its differences from typical SNe Ib.

Findings

Rapid rise to peak brightness in 4.8 days

Early spectra show weak, narrow He I features from CSM interaction

Light curve explained by CSM interaction plus $^{56}$Ni decay

Abstract

This paper describes the rapidly evolving and unusual supernova LSQ13ddu, discovered by the La Silla-QUEST survey. LSQ13ddu displayed a rapid rise of just 4.8$\pm$0.9 d to reach a peak brightness of $-$19.70$\pm$0.02 mag in the $\mathit{LSQgr}$ band. Early spectra of LSQ13ddu showed the presence of weak and narrow He I features arising from interaction with circumstellar material (CSM). These interaction signatures weakened quickly, with broad features consistent with those seen in stripped-envelope SNe becoming dominant around two weeks after maximum. The narrow He I velocities are consistent with the wind velocities of luminous blue variables but its spectra lack the typically seen hydrogen features. The fast and bright early light curve is inconsistent with radioactive $^{56}$Ni powering but can be explained through a combination of CSM interaction and an underlying $^{56}$Ni decay component that dominates the later time behaviour of LSQ13ddu. Based on the strength of the underlying broad features, LSQ13ddu appears deficient in He compared to standard SNe Ib.