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

Abstract

We present photometric and spectroscopic data of the unusual interacting supernova (SN) 2021foa. It rose to an absolute magnitude peak of $M_r=-18$ mag in 20 days. The initial light curve decline shows some luminosity fluctuations before a long-lasting flattening. A faint source ($M_r\sim -14$ mag) was detected in the weeks preceding the main event, showing a slow-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 ($v_{FWHM}\sim$400 km s${}^{-1}$) H emission lines, that, two weeks later, reveal a complex profile, with a narrow P Cygni on top of an intermediate-width ($v_{FWHM}\sim$2700 km s${}^{-1}$) component. At +12 days metal lines in emission appear, while \Hei lines become very strong, with \Hei~$\lambda$5876 reaching half of the \Ha luminosity, much higher than in previous SN 2009ip-like objects. We propose SN 2021foa to be a transitional event between the H-rich SN 2009ip-like SNe and the He-rich Type Ibn SNe.

5 pages, 3 figures, submitted to A&AL after addressing the reviewer's comments

References in corpus (14)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• A giant outburst two years before the core-collapse of a massive star
• SN 2006jc: A Wolf-Rayet Star Exploding in a Dense He-Rich Circumstellar Medium
• Massive stars exploding in a He-rich circumstellar medium. I. Type Ibn (SN 2006jc-like) events
• Massive stars exploding in a He-rich circumstellar medium. II. The transitional case of SN 2005la
• Multi-epoch spectropolarimetry of SN 2009ip: direct evidence for aspherical circumstellar material
• Massive stars exploding in a He-rich circumstellar medium. IV. Transitional Type Ibn Supernovae
• Supernovae 2016bdu and 2005gl, and their link with SN 2009ip-like transients: another piece of the puzzle
• Connecting the progenitors, pre-explosion variability, and giant outbursts of luminous blue variables with Gaia16cfr
• SN 2015bh: NGC 2770's 4th supernova or a luminous blue variable on its way to a Wolf-Rayet star?
• Type Ibn Supernovae May not all Come from Massive Stars
• Photometric and spectroscopic evolution of the interacting transient AT 2016jbu (Gaia16cfr)
• Progenitor, environment, and modelling of the interacting transient, AT 2016jbu (Gaia16cfr)
• Unveiling the Nature of SN 2011fh: a Young and Massive Star Gives Rise to a Luminous SN 2009ip-like Event

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