Ground-based and JWST Observations of SN 2022pul. II. Evidence from Nebular Spectroscopy for a Violent Merger in a Peculiar Type Ia Supernova

Lindsey A. Kwok, Matthew R. Siebert, Joel Johansson, Saurabh W. Jha, Stéphane Blondin, Luc Dessart, Ryan J. Foley, D. John Hillier, Conor Larison, Rüdiger Pakmor, Tea Temim, Jennifer E. Andrews, Katie Auchettl, Carles Badenes, Barna Barnabas, K. Azalee Bostroem, Max J. Brenner Newman, Thomas G. Brink, María José Bustamante-Rosell, Yssavo Camacho-NevesAlejandro Clocchiatti, David A. Coulter, Kyle W. Davis, Maxime Deckers, Georgios Dimitriadis, Yize Dong, Joseph Farah, Alexei V. Filippenko, Andreas Flörs, Ori D. Fox, Peter Garnavich, Estefania Padilla Gonzalez, Or Graur, Franz Josef Hambsch, Griffin Hosseinzadeh, D. Andrew Howell, John P. Hughes, Wolfgang E. Kerzendorf, Xavier K. Saux, Keiichi Maeda, Kate Maguire, Curtis McCully, Cassidy Mihalenko, Megan Newsome, John T. O’Brien, Jeniveve Pearson, Craig Pellegrino, Justin D.R. Pierel, Abigail Polin, Armin Rest, César Rojas-Bravo, David J. Sand, Michaela Schwab, Melissa Shahbandeh, Manisha Shrestha, Nathan Smith, Louis Gregory Strolger, Tamás Szalai, Kirsty Taggart, Giacomo Terreran, Jacco H. Terwel, Samaporn Tinyanont, Stefano Valenti, József Vinkó, J. Craig Wheeler, Yi Yang, Wei Kang Zheng, Chris Ashall, James M. DerKacy, Lluís Galbany, Peter Hoeflich, Thomas de Jaeger, Jing Lu, Justyn Maund, Kyle Medler, Nidia Morell, Benjamin J. Shappee, Maximilian Stritzinger, Nicholas Suntzeff, Michael Tucker, Lifan Wang

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Abstract

We present an analysis of ground-based and JWST observations of SN 2022pul, a peculiar “03fg-like” (or “super-Chandrasekhar”) Type Ia supernova (SN Ia), in the nebular phase at 338 days postexplosion. Our combined spectrum continuously covers 0.4-14 μm and includes the first mid-infrared spectrum of a 03fg-like SN Ia. Compared to normal SN Ia 2021aefx, SN 2022pul exhibits a lower mean ionization state, asymmetric emission-line profiles, stronger emission from the intermediate-mass elements (IMEs) argon and calcium, weaker emission from iron-group elements (IGEs), and the first unambiguous detection of neon in a SN Ia. A strong, broad, centrally peaked [Ne ii] line at 12.81 μm was previously predicted as a hallmark of “violent merger” SN Ia models, where dynamical interaction between two sub-M Ch white dwarfs (WDs) causes disruption of the lower-mass WD and detonation of the other. The violent merger scenario was already a leading hypothesis for 03fg-like SNe Ia; in SN 2022pul it can explain the large-scale ejecta asymmetries seen between the IMEs and IGEs and the central location of narrow oxygen and broad neon. We modify extant models to add clumping of the ejecta to reproduce the optical iron emission better, and add mass in the innermost region (<2000 km s−1) to account for the observed narrow [O i] λ λ6300, 6364 emission. A violent WD-WD merger explains many of the observations of SN 2022pul, and our results favor this model interpretation for the subclass of 03fg-like SNe Ia.

Original languageEnglish (US)
Article number135
JournalAstrophysical Journal
Volume966
Issue number1
DOIs
StatePublished - May 1 2024

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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