A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx
Abstract
We analyse what physical quantities of SN ejecta can be obtained from a single epoch of nebular JWST spectroscopy. We provide an analytical framework, which together with a grid of helium star \texttt{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 105−106 cm−3. This means formation under close to LTE conditions for 200 -- 300 days. We obtain ionisation fractions of Ni and Co, as well as the temperature and filling factor of the Fe/He zone, the 56Ni and stable nickel masses, the Ni/Fe ratio, and the optical depths τ[Ni II] 6.636 μm and τ[Co II] 10.52 μm. 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 MCl I ≃ MCl = 5.1+2.0−1.6× 10−4 M⊙, a factor a few larger than expected from stellar evolution modeling. Furthermore, we find that the SN experienced an unexpectedly small 'Ni-bubble' effect, with ρFeHe = 2.5+0.7−0.4 × 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 MAr II = 4.9+2.2−1.5 × 10−4 M⊙, which from ionisation fractions in our NLTE models yields a best estimate of MAr = 1.1 ± 0.4 × 10−3 M⊙.
Versions
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BibTeX
@misc{barmentloo2026framework,
title = {{A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx}},
author = {S. Barmentloo and A. Jerkstrand},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.32323},
eprint = {2610.32323},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.32323},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx
AU - S. Barmentloo
AU - A. Jerkstrand
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2610.32323
UR - https://arxiv.org/abs/2610.32323
AB - We analyse what physical quantities of SN ejecta can be obtained from a single epoch of nebular JWST spectroscopy. We provide an analytical framework, which together with a grid of helium star \texttt{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 LTE conditions for 200 -- 300 days. We obtain ionisation fractions of Ni and Co, as well as the temperature and filling factor of the Fe/He zone, the ^56Ni and stable nickel masses, the Ni/Fe ratio, and the optical depths τ_[Ni II] 6.636 μm and τ_[Co II] 10.52 μm. 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_Cl I ≃ M_Cl = 5.1^+2.0_−1.6× 10^−4 M_⊙, a factor a few larger than expected from stellar evolution modeling. Furthermore, we find that the SN experienced an unexpectedly small 'Ni-bubble' effect, with ρ_FeHe = 2.5^+0.7_−0.4 × 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_Ar II = 4.9^+2.2_−1.5 × 10^−4 M_⊙, which from ionisation fractions in our NLTE models yields a best estimate of M_Ar = 1.1 ± 0.4 × 10^−3 M_⊙.
ER -