{
  "abstract": "The high-energy end of the gamma-ray burst (GRB) prompt spectrum carries information on the physical conditions of the relativistic outflow, but the number of well-characterized spectral cutoffs is small. We present a systematic search for high-energy spectral cutoffs in the time-integrated prompt spectra of 139 GRBs observed by Fermi between 2008 July and 2025 December, selected to have broadband coverage either through a LAT detection or through bright BGO emission. Joint GBM, LLE, and LAT spectra over $T_{90}$ are fitted with four empirical models and compared using the Bayesian information criterion, yielding 106 bursts with well-constrained cutoff energies $E_c$. An empirical two-component Gaussian mixture model applied to $\\log_{10}(E_c/\\mathrm{MeV})$ separates a low-$E_c$ group from the main distribution at $E_c=2.12$ MeV; the 77 bursts lying firmly above this boundary are interpreted within the internal $γγ$ pair-opacity framework. Combining $E_c$ with wavelet-based minimum variability timescales (median $0.119$ s), we infer bulk Lorentz factors of $11.7$ to $2.78\\times10^{3}$ (median 145) and emission radii of $\\sim10^{13}$ to $10^{15}\\,\\mathrm{cm}$. Neither the $Γ$-$L_{\\mathrm{iso}}$ nor the $Γ$-$E_{\\mathrm{iso}}$ relation is statistically significant for the full sample, whereas the 27 bursts with measured redshifts show a moderate $Γ$-$L_{\\mathrm{iso}}$ correlation with a slope of $0.36_{-0.23}^{+0.22}$. We further find a strong rest-frame correlation between the cutoff and peak energies, $E_{c,z}\\propto E_{p,z}^{2.15_{-0.97}^{+0.96}}$, for the 26 bursts with measured redshifts, which persists after controlling for redshift.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.14411",
  "author_total": 2,
  "authors": [
    {
      "name": "Yuan-Yuan Zuo"
    },
    {
      "name": "Yuan-Chuan Zou"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/a83eyq4551qpp.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.14411",
  "fulltext_url": null,
  "id": "a83eyq4551qpp",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.14411",
  "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"
    ],
    [
      "openalex",
      "3103|Gamma-ray bursts and supernovae"
    ]
  ],
  "openalex": "W7213293071",
  "pdf_url": "https://arxiv.org/pdf/2609.14411",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-13",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/a83eyq4551qpp.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:21:25Z",
      "native_id": "2609.14411",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.14411"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "High-energy spectral cutoffs in the prompt emission of Fermi gamma-ray bursts: bulk Lorentz factors, emission radii, and a cutoff-peak energy relation",
  "title_text": "High-energy spectral cutoffs in the prompt emission of Fermi gamma-ray bursts: bulk Lorentz factors, emission radii, and a cutoff-peak energy relation",
  "type": "preprint",
  "updated_at": "2026-10-30T12:21:25Z",
  "url": "https://research.draconitic.com/paper/a83eyq4551qpp",
  "venue": "arXiv",
  "versions": []
}