A framework for analysing nebular-phase JWST supernova spectra with application to Type Ic SN 2024aecx
Year: 2026
Type: article
Abstract: ABSTRACT We analyse what physical quantities of supernova (SN) ejecta can be obtained from a single epoch of nebular James Webb Space Telescope (JWST) spectroscopy. We provide an analytical framework, which together with a grid of helium star SUMO spectral synthesis models, allows the determination of these quantities for any stripped-envelope SN. Using the framework, we derive critical electron densities for major emission lines, finding values in the range $10^5-10^6$ cm$^{-3}$. This means formation under close to local thermodynamic equilibrium conditions for 200–300 d. We obtain ionization fractions of Ni and Co, as well as the temperature and filling factor of the Fe/He zone, the $^{56}$Ni and stable nickel masses, the Ni/Fe ratio, and the optical depths $\tau _{[\mathrm{ Ni}\, {\small \mathrm{ II}}]\, 6.636}$ and $\tau _{[\mathrm{ Co}\, {\small \mathrm{ II}}]\, 10.52}$. Besides these constraints from iron-group elements, one can also obtain the filling factor of the carbon-burning (O/Ne/Mg) zone from [Ne ii] 12.81 μm, and the masses of Ar ii and Cl i. We apply our methodology to a publicly available JWST spectrum of Type Ic SN 2024aecx. We find that this SN produced a chlorine mass of $M_{\mathrm{Cl\, I}} \simeq M_{\mathrm{Cl}} = 5.1^{+2.0}_{-1.6}\times 10^{-4}$ ${\rm M}_{\odot }$, a factor a few times larger than expected from stellar evolution modelling. Furthermore, we find that the SN experienced an unexpectedly small ‘Ni-bubble’ effect, with $\rho _{\mathrm{FeHe}} = 2.5^{+0.7}_{-0.4} \times 10^{-15}$ g cm$^{-3}$ (or an expansion factor of 1–3 for the Ni-bubble, depending on the adopted model) at 167d for the silicon-burning material. We also determine $M_{\mathrm{Ar\, II}} = 4.9^{+2.2}_{-1.5} \times 10^{-4}$ ${\rm M}_{\odot }$, which, from ionization fractions in our non-local thermodynamic equilibrium models, yields a best estimate of $M_{\mathrm{Ar}} = 1.1 \pm 0.4 \times 10^{-3}$ ${\rm M}_{\odot }$.
Authors: Stan Barmentloo, Anders Jerkstrand
Institutions: Stockholm University, AlbaNova
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
OpenAlex ID: W7223125545