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

DESAI, DHVANIL D.; ASHALL, CHRIS; SHAPPEE, BENJAMIN J.; MORRELL, NIDIA; GALBANY, LLUÍS; BURNS, CHRISTOPHER R.; DERKACY, JAMES M.; HINKLE, JASON T.; HSIAO, ERIC; KUMAR, SAHANA; LU, JING; PHILLIPS, MARK M.; SHAHBANDEH, MELISSA; STRITZINGER, MAXIMILIAN D.; BARON, EDDIE; BERSTEN, MELINA C.; BROWN, PETER J.; DE JAEGER, THOMAS; ELIAS-ROSA, NANCY; FOLATELLI, GASTÓN; HUBER, MARK E.; MAZZALI, PAOLO; MÜLLER-BRAVO, TOMÁS E.; PIRO, ANTHONY L.; POLIN, ABIGAIL; SUNTZEFF, NICHOLAS B.; ANDERSON, JOSEPH P.; CHAMBERS, KENNETH C.; CHEN, TING-WAN; DE BOER, THOMAS; FULTON, MICHAEL D.; GAO, HUA; GROMADZKI, MARIUSZ; INSERRA, COSIMO; MAGNIER, EUGENE A.; NICHOLL, MATT; RAGOSTA, FABIO; WAINSCOAT, RICHARD; YOUNG, DAVID R.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2023 vol. 524 p. 767 - 785

0035-8711

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.