Ground-based and JWST Observations of SN 2022pul. I. Unusual Signatures of Carbon, Oxygen, and Circumstellar Interaction in a Peculiar Type Ia Supernova

Siebert, Matthew and Kwok, Lindsey and Johansson, Joel and Jha, Saurabh W and Blondin, Stéphane and Dessart, Luc and Foley, Ryan and Hillier, Desmond John and Larison, Conor and Pakmor, Ruediger and Temim, Tea and Andrews, J.E. and Auchettl, Katie and Badenes, Carles and Barna, Barnabás and Bostroem, K. Azalee and Newman, Max J. B. and Brink, Thomas G. and Rosell, María José Bustamante and Camacho-Neves, Yssavo and Clocchiatti, Alejandro and Coulter, David and Davis, Kyle and Deckers, Maxime and Dimitriadis, Georgios and Dong, Yize and Farah, Joseph R. and Filippenko, Alexei and Flörs, Andreas and Fox, Ori and Garnavich, Peter and Gonzalez, Estefania Padilla and Graur, Or and Hambsch, Franz-Josef and Hosseinzadeh, Griffin and Howell, D. Andrew and Hughes, John P. and Kerzendorf, Wolfgang and Saux, Xavier Le and Maeda, Keiichi and Maguire, Kate and McCully, Curtis and Mihalenko, Cassidy and Newsome, Megan and O'Brien, John and Pearson, Jeniveve and Pellegrino, Craig and Pierel, Justin R. and Polin, Abigail and Rest, Armin and Rojas-Bravo, Cesar and Sand, David and Schwab, Michaela and Shahbandeh, Melissa and Shrestha, Manisha and Smith, Nathan and Strolger, Louis-Gregory and Szalai, Tamas and Taggart, Kirsty and Terreran, Giacomo and Terwel, Jacco and Tinyanont, Samaporn and VALENTI, Stefano and Vinko, Jozsef and Wheeler, J. Craig and Yang, Yi and Zheng, Weikang and Ashall, Chris and DerKacy, James M and Galbany, Lluís and Hoeflich, Peter and Hsiao, Eric Y. and de Jaeger, Thomas and Lu, Jing and Maund, Justyn and Medler, Kyle and Morrell, Nidia Irene and Shappee, Benjamin and Stritzinger, Maximilian and Suntzeff, Nicholas B. and Tucker, Michael and Wang, Lifan (2024) Ground-based and JWST Observations of SN 2022pul. I. Unusual Signatures of Carbon, Oxygen, and Circumstellar Interaction in a Peculiar Type Ia Supernova. The Astrophysical Journal, 960 (1): ad0975. ISSN 0004-637X

Abstract

Nebular-phase observations of peculiar Type Ia supernovae (SNe Ia) provide important constraints on progenitor scenarios and explosion dynamics for both these rare SNe and the more common, cosmologically useful SNe Ia. We present observations from an extensive ground- and space-based follow-up campaign to characterize SN 2022pul, a super-Chandrasekhar mass SN Ia (alternatively “03fg-like” SN), from before peak brightness to well into the nebular phase across optical to mid-infrared (MIR) wavelengths. The early rise of the light curve is atypical, exhibiting two distinct components, consistent with SN Ia ejecta interacting with dense carbon-oxygen (C/O)-rich circumstellar material (CSM). In the optical, SN 2022pul is most similar to SN 2012dn, having a low estimated peak luminosity (M B = −18.9 mag) and high photospheric velocity relative to other 03fg-like SNe. In the nebular phase, SN 2022pul adds to the increasing diversity of the 03fg-like subclass. From 168 to 336 days after peak B-band brightness, SN 2022pul exhibits asymmetric and narrow emission from [O I] λλ6300, 6364 (FWHM ≈ 2000 km s −1), strong, broad emission from [Ca II] λλ7291, 7323 (FWHM ≈ 7300 km s −1), and a rapid Fe III to Fe II ionization change. Finally, we present the first ever optical-to-MIR nebular spectrum of an 03fg-like SN Ia using data from JWST. In the MIR, strong lines of neon and argon, weak emission from stable nickel, and strong thermal dust emission (with T ≈ 500 K), combined with prominent [O I] in the optical, suggest that SN 2022pul was produced by a white dwarf merger within C/O-rich CSM.