{
  "abstract": "S4 0954+65 (4FGL J0958.7+6534) is a TeV-detected blazar at a redshift of $z = 0.3694 \\pm 0.0011$, classified as an intermediate-synchrotron-peaked BL Lac object. In early 2025, it entered an exceptional $γ$-ray high state. We aim to investigate the origin and physical properties of the exceptional 2025 flare, and to constrain the emission processes responsible for this flaring activity. We performed a multi-wavelength analysis using $γ$-ray, X-ray, optical/UV, radio, and 43 GHz Very Long Baseline Array (VLBA) observations. We examined multi-band correlations with the z-transformed discrete correlation function (zDCF), analyzed the spectral evolution and parsec-scale jet kinematics, and modeled the broadband spectral energy distributions (SEDs). The $γ$-ray variations lead the optical and radio emission by 3.22 days and possibly 18.26 days, respectively, while no significant correlation is found between the $γ$-ray and X-ray emission. The $γ$-ray spectra show a harder-when-brighter behavior, consistent with enhanced particle acceleration during the active state. A similar spectral trend is also observed in the X-ray band, where the photon index is anti-correlated with flux. During the major $γ$-ray flare, VLBA images reveal the emergence of a new superluminal radio knot from the core, whose extrapolated ejection time is consistent with the peak of the $γ$-ray flare. The temporal and structural evolution during the 2025 flare is consistent with a shock-in-jet scenario, in which a newly emerging disturbance propagates downstream and drives the flare. Broadband SED modeling shows that a leptonic synchrotron self-Compton plus external Compton model with dusty torus seed photons reproduces the multi-wavelength observations with physically plausible parameters. A lepto-hadronic interpretation remains possible but requires substantially higher jet power.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.29873",
  "author_total": 14,
  "authors": [
    {
      "name": "Zhihao Ouyang"
    },
    {
      "name": "Jingyu Wu"
    },
    {
      "name": "Hubing Xiao"
    },
    {
      "name": "Lili Yang"
    },
    {
      "name": "Shangchun Xie"
    },
    {
      "name": "Shaohua Zhang"
    },
    {
      "name": "Zhijian Luo"
    },
    {
      "name": "Jianzhen Chen"
    },
    {
      "name": "Jianguo Wang"
    },
    {
      "name": "Mingjun Liu"
    },
    {
      "name": "Qinyu Wu"
    },
    {
      "name": "Huaqing Cheng"
    },
    {
      "name": "Wenda Zhang"
    },
    {
      "name": "Junhui Fan"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/9s9zvqy3ksmmm.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.29873",
  "fulltext_url": null,
  "id": "9s9zvqy3ksmmm",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.29873",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.GA"
    ],
    [
      "arxiv",
      "astro-ph.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2609.29873",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-24",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/9s9zvqy3ksmmm.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:11Z",
      "native_id": "2609.29873",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.29873"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Exceptional Gamma-Ray Flaring Activity of the Blazar S4 0954+65 in Early 2025",
  "title_text": "Exceptional Gamma-Ray Flaring Activity of the Blazar S4 0954+65 in Early 2025",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:11Z",
  "url": "https://research.draconitic.com/paper/9s9zvqy3ksmmm",
  "venue": "arXiv",
  "versions": []
}