{
  "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 $10^5-10^6$ 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 $^{56}$Ni and stable nickel masses, the Ni/Fe ratio, and the optical depths $τ_{\\mathrm{[Ni\\,II]\\, 6.636 μm}}$ and $τ_{\\mathrm{[Co\\,II]\\, 10.52 μm}}$. 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 $μ$m, 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 $M_{\\mathrm{Cl\\, I}} \\simeq M_{\\mathrm{Cl}} = 5.1^{+2.0}_{-1.6}\\times 10^{-4}$ $M_{\\odot}$, 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 $ρ_{\\mathrm{FeHe}} = 2.5^{+0.7}_{-0.4} \\times 10^{-15}$ 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 $M_{\\mathrm{Ar\\, II}} = 4.9^{+2.2}_{-1.5} \\times 10^{-4}$ $M_{\\odot}$, which from ionisation fractions in our NLTE models yields a best estimate of $M_{\\mathrm{Ar}} = 1.1 \\pm 0.4 \\times 10^{-3}$ $M_{\\odot}$.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.32323",
  "author_total": 2,
  "authors": [
    {
      "name": "S. Barmentloo"
    },
    {
      "name": "A. Jerkstrand"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/78h258w4sgdxq.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.32323",
  "fulltext_url": null,
  "id": "78h258w4sgdxq",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.32323",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.HE"
    ],
    [
      "arxiv",
      "astro-ph.SR"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2610.32323",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-23",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/78h258w4sgdxq.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:35:15Z",
      "native_id": "2610.32323",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.32323"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.SR",
      "subfield": "stellar"
    }
  ],
  "title": "A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx",
  "title_text": "A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx",
  "type": "preprint",
  "updated_at": "2026-10-30T12:35:15Z",
  "url": "https://research.draconitic.com/paper/78h258w4sgdxq",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1093/mnras/stag1990",
      "pid": "ay4z1b38kczgv",
      "relation": "published-as",
      "title": "A Framework for Analysing Nebular-Phase JWST Supernova Spectra with Application to Type Ic SN 2024aecx",
      "venue": "Monthly Notices of the Royal Astronomical Society"
    }
  ]
}