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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx

  • Stan Barmentloo1
  • Anders Jerkstrand1
  1. 1Stockholm University The Oskar Klein Centre, Department of Astronomy, , AlbaNova, SE-10691 Stockholm ,
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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 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 small II] 6.636 and τ [Co small 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 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 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 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⊙.

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Cite

BibTeXRIS
BibTeX
@article{barmentloo2026framework,
  title = {{A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx}},
  author = {Stan Barmentloo and Anders Jerkstrand},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag1990},
  url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1990/8965454},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx
AU  - Stan Barmentloo
AU  - Anders Jerkstrand
PY  - 2026
DA  - 2026/10/21
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag1990
UR  - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1990/8965454
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 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 small II] 6.636 and τ _[Co small 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_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 MAr = 1.1 ± 0.4 × 10−3 M⊙.
SN  - 0035-8711
SN  - 1365-2966
ER  -