[2108.07278]
Morgan Fraser, Maximilian D. Stritzinger, Sean J. Brennan, Andrea Pastorello, Yongzhi Cai, Anthony L. Piro, Chris Ashall, Peter Brown, Christopher R. Burns, Nancy Elias-Rosa, Rubina Kotak, Alexei V. Filippenko, L. Galbany, E. Y. Hsiao, Saurabh W. Jha, Andrea Reguitti, Ju-jia Zhang, Shane Moran, Nidia Morrell, B. J. Shappee, Lina Tomasella, J. P. Anderson, Tyler Barna, Paolo Ochner, M. M. Phillips, Michael Tucker, Xiaofeng Wang, E. Baron, Stefano Benetti, Melina C. Bersten, Thomas G. Brink, Yssavo Camacho-Neves, Scott Davis, Kyle G. Dettman, Gaston Folatelli, Claudia P. Gutierrez, Peter Hoflich, Thomas W. -S. Holoien, Erkki Kankare, Sahana Kumar, Jing Lu, Paolo Mazzali, Stefan Taubenberger, Samaporn Tinyanont, Hanindyo Kuncarayakti, Lindsey Kwok, Melissa Shahbandeh, Nicholas B. Suntzeff, Shengyu Yan, Yi Yang, WeiKang Zheng
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$^{-1}$. 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 ($4\times10^{51}$ erg) explosion of a stripped star, producing 0.4 M$_\odot$ of 56Ni within a $\sim$1 M$_\odot$ shell of CSM extending out to 400 R$_\odot$.