SN 2021foa: Deriving a continuity between SN IIn and SN Ibn

• Published in: arXiv.org 2024-09
• Main Authors: Gangopadhyay, Anjasha, Dukiya, Naveen, Moriya, Takashi J, Tanaka, Masaomi, Maeda, Keiichi, Howell, D Andrew, Singh, Mridweeka, Singh, Avinash, Sollerman, Jesper, Kawabata, Koji S, Brennan, Sean J, Pellegrino, Craig, Dastidar, Raya, Nakaoka, Tatsuya, Kawabata, Miho, Misra, Kuntal, Schulze, Steve, Chandra, Poonam, Taguchi, Kenta, Sahu, Devendra K, McCully, Curtis, Bostroem, K Azalee, Estefania Padilla Gonzalez, Newsome, Megan, Hiramatsu, Daichi, Takei, Yuki, Yamanaka, Masayuki, Tajitsu, Akito, Isogai, Keisuke
• Format: Article
• Language: English
• Subjects: Binary stars; Ejecta; Evolution; Light curve; Line spectra; Luminosity; Photometry; Variable stars; Wind speed
• ISSN: 2331-8422

We present the long-term photometric and spectroscopic analysis of a transitioning SN~IIn/Ibn from \(-\)10.8 d to 150.7 d post \(V\)-band maximum. SN~2021foa shows prominent He {\sc i} lines comparable in strength to the H\(\alpha\) line around peak, placing SN~2021foa between the SN~IIn and SN~Ibn populations. The spectral comparison shows that it resembles the SN~IIn population at pre-maximum, becomes intermediate between SNe~IIn/Ibn and at post-maximum matches with SN~IIn 1996al. The photometric evolution shows a precursor at \(-\)50 d and a light curve shoulder around 17d. The peak luminosity and color evolution of SN 2021foa are consistent with most SNe~IIn and Ibn in our comparison sample. SN~2021foa shows the unique case of a SN~IIn where the narrow P-Cygni in H\(\alpha\) appear at later stages. The H\(\alpha\) profile consists of a narrow (500 -- 1200 km s\(^{-1}\)) component, intermediate width (3000 -- 8000 km s\(^{-1}\)) and broad component in absorption. Temporal evolution of the H\(\alpha\) profile favours a disk-like CSM geometry. Hydrodynamical modelling of the lightcurve well reproduces a two-component CSM structure with different densities (\(\rho\) \(\propto\) r\(^{-2}\) -- \(\rho\) \(\propto\) r\(^{-5}\)), mass-loss rates (10\(^{-3}\) -- 10\(^{-1}\) M\(_{\odot}\) yr\(^{-1}\)) assuming a wind velocity of 1000 km s\(^{-1}\) and having a CSM mass of 0.18 M\(_{\odot}\). The overall evolution indicates that SN~2021foa most likely originated from a LBV star transitioning to a WR star with the mass-loss rate increasing in the period from 5 to 0.5 years before the explosion or it could be due to a binary interaction.