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

D. Farias, C. Gall, G. Narayan, S. Rest, V. A. Villar, C. R. Angus, K. Auchettl, K. W. Davis, R. J. Foley, A. Gagliano, J. Hjorth, L. Izzo, C. D. Kilpatrick, H. M.L. Perkins, E. Ramirez-Ruiz, C. L. Ransome, A. Sarangi, R. Yarza, D. A. Coulter, D. O. JonesN. Khetan, A. Rest, M. R. Siebert, J. J. Swift, K. Taggart, S. Tinyanont, P. Wrubel, T. J.L. de Boer, K. E. Clever, A. Dhara, H. Gao, C. C. Lin

Research output: Contribution to journalArticlepeer-review

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.

Original languageEnglish (US)
Article number152
JournalAstrophysical Journal
Volume977
Issue number2
DOIs
StatePublished - Dec 1 2024

Funding

This investigation is based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 107.22RH (PI: C. Gall) and 109.23K3 (PI: D. Farias). Research at Lick Observatory is partially supported by a generous gift from Google. Based in part on observations obtained at the SOAR telescope, which is a joint project of the Minist\u00E9rio da Ci\u00EAncia, Tecnologia e Inova\u00E7\u00F5es (MCTI/LNA) do Brasil, the US National Science Foundation's NOIRLab, the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU). The data presented here were obtained in part with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOT. We acknowledge the use of public data from the Swift data archive. This work makes use of data taken with the Las Cumbres Observatory global telescope network. The LCO group is funded by NSF grants AST-1911151 and AST-1911225. This work has made use of data from the ATLAS project. ATLAS is primarily funded to search for near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen\u2019s University Belfast, and the Space Telescope Science Institute. This work is based in part on data obtained at the Infrared Telescope Facility, which is operated by the University of Hawaii under contract 80HQTR24DA010 with NASA. This work is supported by a VILLUM FONDEN Young Investigator Grant (project number 25501) and by research grants (VIL16599, VIL54489) from VILLUM FONDEN. C.R.A. is supported by the European 1172 Research Council (ERC) under the European Union's 1173 Horizon 2020 research and innovation program (grant 1174 agreement No. 948381). V.A.V. acknowledges support from the National Science Foundation (NSF) through grant AST\u20132108676. This work is supported by the NSF under Cooperative Agreement PHY-2019786 (The NSF AI Institute for Artificial Intelligence and Fundamental Interactions, http://iaifi.org/ ). Parts of this research were supported by the Australian Research Council Discovery Early Career Researcher Award (DECRA) through project No. DE230101069. The UCSC team is supported in part by NASA grant 80NSSC20K0953, NSF grant AST-1815935, the Gordon and Betty Moore Foundation, the Heising-Simons Foundation, and by a fellowship from the David and Lucile Packard Foundation to R.J.F. R.Y. received support from a Doctoral Fellowship from the University of California Institute for Mexico and the United States (UCMEXUS) and a NASA FINESST award (21-ASTRO21-0068) postdoctoral fellowship. G.N. gratefully acknowledges NSF support from AST-2206195 for this work. G.N. is also supported by NSF CAREER grant AST-2239364, supported in part by funding from Charles Simonyi, and NSF OAC-2311355, DOE support through the Department of Physics at the University of Illinois, Urbana-Champaign (13771275), and support from the HST Guest Observer Program through HST-GO-16764 and HST-GO-17128 (PI: R. Foley). This work was performed in part at the Aspen Center for Physics, which is supported by NSF grant PHY-2210452. YSE-PZ was developed by the UC Santa Cruz Transients Team. The UCSC team is supported in part by NASA grants NNG17PX03C, 80NSSC19K1386, and 80NSSC20K0953; NSF grants AST-1518052, AST-1815935, and AST-1911206; the Gordon & Betty Moore Foundation; the Heising-Simons Foundation; a fellowship from the David and Lucile Packard Foundation to R.J.F.; Gordon and Betty Moore Foundation postdoctoral fellowships and a NASA Einstein Fellowship, as administered through the NASA Hubble Fellowship program and grant HST-HF2-51462.001, to D.O.J.; and an NSF Graduate Research Fellowship, administered through grant DGE-1339067, to D.A.C.

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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