SN 2021foa: The “Flip-flop” Type IIn/Ibn Supernova

Abstract We present a comprehensive analysis of the photometric and spectroscopic evolution of SN 2021foa, unique among the class of transitional supernovae for repeatedly changing its spectroscopic appearance from hydrogen-to-helium-to-hydrogen dominated (IIn-to-Ibn-to-IIn) within 50 days past peak brightness. The spectra exhibit multiple narrow (≈300–600 km s −1 ) absorption lines of hydrogen, helium, calcium, and iron together with broad helium emission lines with a full width at half-maximum (FWHM) of ∼6000 km s −1 . For a steady, wind mass-loss regime, light-curve modeling results in an ejecta mass of ∼8 M ⊙ and circumstellar material (CSM) mass below 1 M ⊙ , and an ejecta velocity consistent with the FWHM of the broad helium lines. We obtain a mass-loss rate of ≈2 M ⊙ yr −1 . This mass-loss rate is 3 orders of magnitude larger than derived for normal Type II supernovae. We estimate that the bulk of the CSM of SN 2021foa must have been expelled within half a year, about 12 yr ago. Our analysis suggests that SN 2021foa had a helium-rich ejecta that swept up a dense shell of hydrogen-rich CSM shortly after explosion. At about 60 days past peak brightness, the photosphere recedes through the dense ejecta-CSM region, occulting much of the redshifted emission of the hydrogen and helium lines, which results in an observed blueshift (∼−3000 km s −1 ). Strong mass-loss activity prior to explosion, such as those seen in SN 2009ip-like objects and SN 2021foa as precursor emission, are the likely origin of a complex, multiple-shell CSM close to the progenitor star.

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Publication Details

Journal
The Astrophysical Journal
Published
2024-12-01
DOI
https://doi.org/10.3847/1538-4357/ad8cd3
Citations
8
Primary Topic
Gamma-ray bursts and supernovae
Type
article
Field-Weighted Citation Impact
2.65

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article

SN 2021foa: The “Flip-flop” Type IIn/Ibn Supernova

R. J. Foley, C. D. Kilpatrick, J. Hjorth, D. O. Jones et al.
8 citations
The Astrophysical Journal
Gamma-ray bursts and supernovae
2.65
article

SN 2021foa: The “Flip-flop” Type IIn/Ibn Supernova

R. J. Foley, C. D. Kilpatrick, J. Hjorth, D. O. Jones, Christa Gall, C. L. Ransome, Gautham Narayan, Ricardo Yarza, Thomas de Boer, N. Khetan, A. Rest, Chien-Cheng Lin, E. Ramírez-Ruiz, Kyle W. Davis, Matthew R. Siebert, Jonathan Swift, Samaporn Tinyanont, Arkaprabha Sarangi, V. Ashley Villar, D. Farias, C. R. Angus, Alexander Gagliano, K. Taggart, Atirath Dhara, Haille M. L. Perkins, S. Rest, D. A. Coulter, Luca Izzo, Katie Auchettl, K. E. Clever, Hua Gao, P. Wrubel
article en
8 citations

Abstract

Abstract We present a comprehensive analysis of the photometric and spectroscopic evolution of SN 2021foa, unique among the class of transitional supernovae for repeatedly changing its spectroscopic appearance from hydrogen-to-helium-to-hydrogen dominated (IIn-to-Ibn-to-IIn) within 50 days past peak brightness. The spectra exhibit multiple narrow (≈300–600 km s −1 ) absorption lines of hydrogen, helium, calcium, and iron together with broad helium emission lines with a full width at half-maximum (FWHM) of ∼6000 km s −1 . For a steady, wind mass-loss regime, light-curve modeling results in an ejecta mass of ∼8 M ⊙ and circumstellar material (CSM) mass below 1 M ⊙ , and an ejecta velocity consistent with the FWHM of the broad helium lines. We obtain a mass-loss rate of ≈2 M ⊙ yr −1 . This mass-loss rate is 3 orders of magnitude larger than derived for normal Type II supernovae. We estimate that the bulk of the CSM of SN 2021foa must have been expelled within half a year, about 12 yr ago. Our analysis suggests that SN 2021foa had a helium-rich ejecta that swept up a dense shell of hydrogen-rich CSM shortly after explosion. At about 60 days past peak brightness, the photosphere recedes through the dense ejecta-CSM region, occulting much of the redshifted emission of the hydrogen and helium lines, which results in an observed blueshift (∼−3000 km s −1 ). Strong mass-loss activity prior to explosion, such as those seen in SN 2009ip-like objects and SN 2021foa as precursor emission, are the likely origin of a complex, multiple-shell CSM close to the progenitor star.

The Astrophysical JournalVol. 977(2)
Northwestern University (US), University of Copenhagen (DK), Queen's University Belfast (GB), Space Telescope Science Institute (US), University of Hawaii System (US), Johns Hopkins University (US), University of Illinois Urbana-Champaign (US), The University of Queensland (AU), The University of Melbourne (AU), University of California, Santa Cruz (US), Astronomical Observatory of Capodimonte (IT), University of Hawaii at Hilo (US), Université Bourgogne Franche-Comté (FR), Center for Astrophysics Harvard & Smithsonian (US), The NSF AI Institute for Artificial Intelligence and Fundamental Interactions (US), Massachusetts Institute of Technology (US), National Astronomical Research Institute of Thailand (TH)
National Science Foundation, National Aeronautics and Space Administration, Villum Fonden, HORIZON EUROPE European Research Council
Openalex Percentile: Top 10%
Gamma-ray bursts and supernovae
2.65
DOIOpen Access PDFOpenAlex
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