Fast and not-so-furious: Case study of the fast and faint Type IIb SN 2021bxu

Dhvanil D. Desai, Chris Ashall, Benjamin J. Shappee, Nidia Morrell, Lluís Galbany, Christopher R. Burns, James M. Derkacy, Jason T. Hinkle, Eric Hsiao, Sahana Kumar, Jing Lu, Mark M. Phillips, Melissa Shahbandeh, Maximilian D. Stritzinger, Eddie Baron, Melina C. Bersten, Peter J. Brown, Thomas De Jaeger, Nancy Elias-Rosa, Gastón FolatelliMark E. Huber, Paolo Mazzali, Tomás E. Müller-Bravo, Anthony L. Piro, Abigail Polin, Nicholas B. Suntzeff, Joseph P. Anderson, Kenneth C. Chambers, Ting Wan Chen, Thomas De Boer, Michael D. Fulton, Hua Gao, Mariusz Gromadzki, Cosimo Inserra, Eugene A. Magnier, Matt Nicholl, Fabio Ragosta, Richard Wainscoat, David R. Young

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


We present photometric and spectroscopic observations and analysis of SN 2021bxu (ATLAS21dov), a low-luminosity, fast-evolving Type IIb supernova (SN). SN 2021bxu is unique, showing a large initial decline in brightness followed by a short plateau phase. With during the plateau, it is at the lower end of the luminosity distribution of stripped-envelope supernovae (SE-SNe) and shows a distinct ∼10 d plateau not caused by H- or He-recombination. SN 2021bxu shows line velocities which are at least slower than typical SE-SNe. It is photometrically and spectroscopically similar to Type IIb SNe during the photospheric phases of evolution, with similarities to Ca-rich IIb SNe. We find that the bolometric light curve is best described by a composite model of shock interaction between the ejecta and an envelope of extended material, combined with a typical SN IIb powered by the radioactive decay of 56Ni. The best-fitting parameters for SN 2021bxu include a 56Ni mass of, an ejecta mass of, and an ejecta kinetic energy of. From the fits to the properties of the extended material of Ca-rich IIb SNe we find a trend of decreasing envelope radius with increasing envelope mass. SN 2021bxu has MNi on the low end compared to SE-SNe and Ca-rich SNe in the literature, demonstrating that SN 2021bxu-like events are rare explosions in extreme areas of parameter space. The progenitor of SN 2021bxu is likely a low-mass He star with an extended envelope.

Original languageEnglish
Pages (from-to)767-785
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
StatePublished - 1 Sep 2023


  • stars: massive
  • supernovae: general
  • supernovae: individual: SN 2021bxu


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