SN 2021foa, a transitional event between a Type IIn (SN 2009ip-like) and a Type Ibn supernova

Reguitti, A ORCID: 0000-0003-4254-2724, Pastorello, A ORCID: 0000-0002-7259-4624, Pignata, G, Fraser, M ORCID: 0000-0003-2191-1674, Stritzinger, MD ORCID: 0000-0002-5571-1833, Brennan, SJ, Cai, YZ ORCID: 0000-0002-7714-493X, Elias-Rosa, N ORCID: 0000-0002-1381-9125, Fugazza, D, Gutierrez, CP ORCID: 0000-0003-2375-2064, Kankare, E, Kotak, R, Lundqvist, P, Mazzali, PA ORCID: 0000-0001-6876-8284, Moran, S, Salmaso, I, Tomasella, L ORCID: 0000-0002-3697-2616, Valerin, G and Kuncarayakti, H (2022) SN 2021foa, a transitional event between a Type IIn (SN 2009ip-like) and a Type Ibn supernova. Astronomy and Astrophysics, 662. ISSN 0004-6361

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Abstract

We present photometric and spectroscopic data of the unusual interacting supernova (SN) 2021foa. It rose to an absolute magnitude peak of Mr= 18 mag in 20 days. The initial light curve decline shows some luminosity fluctuations before a long-lasting flattening. A faint source (Mr∼ 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 (∼400 km s1) H emission lines that, two weeks later, reveal a complex profile, with a narrow P Cygni on top of an intermediate-width (∼2700 km s1) component. At +12 days, metal lines in emission appear and Hea lines become very strong, with Hea λ5876 reaching half of the Hα 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.

Item Type:	Article
Uncontrolled Keywords:	0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects:	Q Science > QB Astronomy
Divisions:	Astrophysics Research Institute
Publisher:	EDP Sciences
Date of acceptance:	5 June 2022
Date of first compliant Open Access:	1 November 2022
Date Deposited:	01 Nov 2022 16:59
Last Modified:	05 Jul 2025 12:45
DOI or ID number:	10.1051/0004-6361/202243340
URI:	https://researchonline.ljmu.ac.uk/id/eprint/17997

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