We present observations of SN 2021csp, a unique supernova (SN) which displays evidence for interaction with H- and He- poor circumstellar material (CSM) at early times. Using high-cadence spectroscopy taken over the first week after explosion, we show that the spectra of SN 2021csp are dominated by C III lines with a velocity of 1800 km/s. We associate this emission with CSM lost by the progenitor prior to explosion. Subsequently, the SN displays narrow He lines before metamorphosing into a broad-lined Type Ic SN. We model the bolometric light curve of SN 2021csp, and show that it is consistent with the energetic (4×10⁵¹ erg) explosion of a stripped star, producing 0.4M_⊙ of ⁵⁶Ni within a ∼1 M_⊙ shell of CSM extending out to 400 R_⊙.

https://ui.adsabs.harvard.edu/abs/2021arXiv210807278F