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

This paper presents an analysis of ground-based and JWST observations of SN 2022pul, a peculiar Type Ia supernova (SN Ia), in the nebular phase. The combined spectrum (0.4-14 µm) reveals a lower mean ionization state, asymmetric emission-line profiles, stronger intermediate-mass element (IME) emission (argon and calcium), weaker iron-group element (IGE) emission, and the first unambiguous detection of neon in a SN Ia. The strong, broad, centrally peaked [Ne II] line at 12.81 µm supports the "violent merger" SN Ia model, where interaction between two sub-Chandrasekhar mass white dwarfs (WDs) leads to disruption of one and detonation of the other. This model explains the ejecta asymmetries and the central location of oxygen and broad neon. Modifications to existing models, including ejecta clumping and added mass in the innermost region, improve the fit to the observed spectrum. The findings strongly favor a violent WD-WD merger as the origin of SN 2022pul and this subclass of 03fg-like SNe Ia.

Kw, Jo, Luc Dessart, T Temim, Andr, Au, Bad, G Br, Ca, Clo, Lindsey A Kwok