Circumstellar Interaction Powers the Light Curves of Luminous Rapidly Evolving Optical Transients

TL;DR

This study demonstrates that circumstellar interaction with dense CSM shells can power the light curves of luminous, rapidly evolving transients and Type Ibn supernovae, unifying their understanding through a common model.

Contribution

It introduces a unified analytical model explaining the light curves of both Type Ibn SNe and rapidly evolving transients via ejecta-CSM interaction, a novel approach in the field.

Findings

Models with specific ejecta and CSM masses reproduce observed light curves.

A common progenitor system can explain diverse transient behaviors.

The model successfully reproduces light curves of AT 2018cow and similar objects.

Abstract

Rapidly evolving transients, or objects that rise and fade in brightness on timescales two to three times shorter than those of typical Type Ia or Type II supernovae (SNe), have uncertain progenitor systems and powering mechanisms. Recent studies have noted similarities between rapidly evolving transients and Type Ibn SNe, which are powered by ejecta interacting with He-rich circumstellar material (CSM). In this work we present multiband photometric and spectroscopic observations from Las Cumbres Observatory and Swift of four fast-evolving Type Ibn SNe. We compare these observations with those of rapidly evolving transients identified in the literature. We discuss several common characteristics between these two samples, including their light curve and color evolution as well as their spectral features. To investigate a common powering mechanism we construct a grid of analytical model light curves with luminosity inputs from CSM interaction as well as $^{56}$Ni radioactive decay. We find that models with ejecta masses of $\approx 1-3$ M$_\odot$, CSM masses of $\approx 0.2-1$ M$_\odot$, and CSM radii of $\approx 20-65$ au can explain the diversity of peak luminosities, rise times, and decline rates observed in Type Ibn SNe and rapidly evolving transients. This suggests that a common progenitor system$-$the core collapse of a high-mass star within a dense CSM shell$-$can reproduce the light curves of even the most luminous and fast-evolving objects, such as AT 2018cow. This work is one of the first to reproduce the light curves of both SNe Ibn and other rapidly evolving transients with a single model.