The Type Icn SN 2021csp: Implications for the Origins of the Fastest Supernovae and the Fates of Wolf-Rayet Stars
Kulkarni, S. R.; Filippenko, Alexei V.; Duev, Dmitry A.; Riddle, Reed; Baade, Dietrich; Sollerman, Jesper; Perley, Daniel A.; Andreoni, Igor; Bellm, Eric C.; Dekany, Richard; Fremling, Christoffer; Kasliwal, Mansi M.; Masci, Frank J.; Shupe, David L.; Lunnan, Ragnhild; Ho, Anna Y. Q.; Yang, Yi; Yao, Yuhan; Schulze, Steve; Gal-Yam, Avishay; Zheng, WeiKang; Brink, Thomas G.; Coughlin, Michael W.; Yan, Lin; Maund, Justyn R.; Kool, Erik C.; Rosnet, Philippe; Chen, Ting-Wan; Tzanidakis, Anastasios; Strotjohann, Nora Linn; Irani, Ido; Hoeflich, Peter; Cikota, Aleksandar; Medford, Michael S.; Dahiwale, Aishwarya
United Kingdom, Sweden, United States, Israel, Germany, Chile, France
Abstract
We present observations of SN 2021csp, the second example of a newly identified type of supernova (SN) hallmarked by strong, narrow, P Cygni carbon features at early times (Type Icn). The SN appears as a fast and luminous blue transient at early times, reaching a peak absolute magnitude of -20 within 3 days due to strong interaction between fast SN ejecta (v ≈ 30,000 km s-1) and a massive, dense, fast-moving C/O wind shed by the WC-like progenitor months before explosion. The narrow-line features disappear from the spectrum 10-20 days after explosion and are replaced by a blue continuum dominated by broad Fe features, reminiscent of Type Ibn and IIn supernovae and indicative of weaker interaction with more extended H/He-poor material. The transient then abruptly fades ~60 days post-explosion when interaction ceases. Deep limits at later phases suggest minimal heavy-element nucleosynthesis, a low ejecta mass, or both, and imply an origin distinct from that of classical Type Ic SNe. We place SN 2021csp in context with other fast-evolving interacting transients, and discuss various progenitor scenarios: an ultrastripped progenitor star, a pulsational pair-instability eruption, or a jet-driven fallback SN from a Wolf-Rayet (W-R) star. The fallback scenario would naturally explain the similarity between these events and radio-loud fast transients, and suggests a picture in which most stars massive enough to undergo a W-R phase collapse directly to black holes at the end of their lives.