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 56Ni radioactive decay. We find that
models with ejecta masses of ≈1–3 Me, CSM masses of ≈0.2–1 Me, and CSM radii of ≈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.
