{
  "abstract": "Extragalactic fast X-ray transients (EFXTs) detected by the Einstein Probe are extending the parameter space of relativistic stellar explosions toward softer and longer-lived transients. Here we report EP251129a/GRB 251129A at z=0.505, which exhibits two X-ray plateaus: an early plateau lasting $\\sim 10^{4}\\,\\rm s$ followed by a rapid decay with spectral softening, and a second plateau extending to 60 days, placing it at the extreme long-duration end of Gamma Ray Burst (GRB) plateaus. The early optical emission evolves independently of the X-ray, indicating a different origin; whereas the unusual radio afterglow shows a rapid rise of $F_ν\\propto t^{1.9-2.5}$ and a delayed peak at $\\sim36-40$ days, providing strong evidence for an off-axis geometry. We find that the early X-ray behavior resembles those of ultra-long GRBs (ULGRBs) and can be naturally explained by the internal dissipation from a newborn millisecond magnetar undergoing gravitational-wave-dominated spin-down before collapsing into a black hole. The early optical, radio and late X-ray emission are well described by an off-axis two-component jet afterglow with additional energy injection, possibly powered by fallback accretion onto black hole. EP251129a therefore connects the emerging EFXT population with ULGRB-like central-engine activity and off-axis afterglow, offering a rare opportunity to probe both the evolution of central engine and jet structure in a single event.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.34810",
  "author_total": 27,
  "authors": [
    {
      "name": "Yue Wu"
    },
    {
      "name": "Ailing Wang"
    },
    {
      "name": "Senlin Pang"
    },
    {
      "name": "Yu-Han Yang"
    },
    {
      "name": "Biao Zhang"
    },
    {
      "name": "Zi-Gao Dai"
    },
    {
      "name": "Tao An"
    },
    {
      "name": "Jin-Jun Geng"
    },
    {
      "name": "Xue-Feng Wu"
    },
    {
      "name": "Hui Sun"
    },
    {
      "name": "Di Xiao"
    },
    {
      "name": "Jia Ren"
    },
    {
      "name": "Chen Deng"
    },
    {
      "name": "Yehao Cheng"
    },
    {
      "name": "Fa-Yin Wang"
    },
    {
      "name": "Yuan-Pei Yang"
    },
    {
      "name": "Eleonora Troja"
    },
    {
      "name": "Brendan O'Connor"
    },
    {
      "name": "Wen-Jie Zhang"
    },
    {
      "name": "Yuan Liu"
    },
    {
      "name": "Weimin Yuan"
    },
    {
      "name": "Yahui Jiang"
    },
    {
      "name": "Yun Wang"
    },
    {
      "name": "Cuiyuan Dai"
    },
    {
      "name": "Hucheng Ding"
    },
    {
      "name": "Tao Wu"
    },
    {
      "name": "Kangrui Ni"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/cyf06mbtfc7w2.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.34810",
  "fulltext_url": null,
  "id": "cyf06mbtfc7w2",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.34810",
  "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.HE"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2610.34810",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-26",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/cyf06mbtfc7w2.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:35:35Z",
      "native_id": "2610.34810",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.34810"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "EP251129a: A Fast X-ray Transient with Two X-Ray Plateaus and Its Off-axis Afterglow",
  "title_text": "EP251129a: A Fast X-ray Transient with Two X-Ray Plateaus and Its Off-axis Afterglow",
  "type": "preprint",
  "updated_at": "2026-10-30T12:35:35Z",
  "url": "https://research.draconitic.com/paper/cyf06mbtfc7w2",
  "venue": "arXiv",
  "versions": []
}