SN 2021foa, a transitional event between a Type IIn (SN 2009ip-like) and a Type Ibn supernova
: Reguitti A, Pastorello A, Pignata G, Fraser M, Stritzinger MD, Brennan SJ, Cai YZ, Elias-Rosa N, Fugazza D, Gutierrez CP, Kankare E, Kotak R, Lundqvist P, Mazzali PA, Moran S, Salmaso I, Tomasella L, Valerin G, Kuncarayakti H
Publisher: EDP SCIENCES S A
: 2022
: Astronomy and Astrophysics
: ASTRONOMY & ASTROPHYSICS
: ASTRON ASTROPHYS
: L10
: 662
: 13
: 0004-6361
: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202243340
: https://doi.org/10.1051/0004-6361/202243340
: https://research.utu.fi/converis/portal/detail/Publication/176022838
We present photometric and spectroscopic data of the unusual interacting supernova (SN) 2021foa. It rose to an absolute magnitude peak of M-r & x2004;=& x2004;-18 mag in 20 days. The initial light curve decline shows some luminosity fluctuations before a long-lasting flattening. A faint source (M-r & x2004;similar to & x2004;-14 mag) was detected in the weeks preceding the main event, showing a slowly rising luminosity trend. The r-band absolute light curve is very similar to those of SN 2009ip-like events, with a faint and shorter duration brightening ('Event A') followed by a much brighter peak ('Event B'). The early spectra of SN 2021foa show a blue continuum with narrow (similar to 400 km s(-1)) H emission lines that, two weeks later, reveal a complex profile, with a narrow P Cygni on top of an intermediate-width (similar to 2700 km s(-1)) component. At +12 days, metal lines in emission appear and He I lines become very strong, with He I lambda 5876 reaching half of the H alpha luminosity, much higher than in previous SN 2009ip-like objects. We propose that SN 2021foa is a transitional event between the H-rich SN 2009ip-like SNe and the He-rich Type Ibn SNe.
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