{
  "abstract": "Gamma-ray quiet fast X-ray transients (FXTs) provide a new approach for studying relativistic explosions that evade traditional gamma-ray triggers. In this work, we present multi-wavelength observations and analysis of EP260119a, a high-$z$ FXT detected by Einstein Probe/WXT and followed up with COLIBRÍ, the Liverpool Telescope, and other facilities. Spectroscopy yields a redshift of $z = 5.47$, making EP260119a the most distant FXT detected by Einstein Probe to date. Despite its luminous X-ray and optical emission, no prompt gamma-ray counterpart was detected by SVOM/ECLAIRs, SVOM/GRM, Swift/BAT, or Konus/Wind, despite contemporaneous coverage. The broadband afterglow is well described by synchrotron emission from a uniform relativistic jet propagating into a shallowly stratified external medium close to the constant-density limit, indicating a standard relativistic explosion despite the absence of detectable gamma rays. Occupying the extreme high-$z$ end of the growing Einstein Probe FXT sample, EP260119a supports the possibility that soft X-ray surveys are uncovering relativistic transients that remain undetected by current gamma-ray instruments. Our results indicate that some explosions in the early Universe escape conventional gamma-ray surveys and demonstrate the value of combining sensitive soft X-ray discovery with rapid optical follow-up to obtain a more complete view of the high-$z$ transient population.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.27127",
  "author_total": 44,
  "authors": [
    {
      "name": "Camila Angulo-Valdez"
    },
    {
      "name": "Asuka Kuwata"
    },
    {
      "name": "Edilberto Aguilar-Ruiz"
    },
    {
      "name": "Rosa L Becerra"
    },
    {
      "name": "Ramandeep Gill"
    },
    {
      "name": "Miguel Angel Aloy"
    },
    {
      "name": "Antonio de Ugarte Postigo"
    },
    {
      "name": "Alan M Watson"
    },
    {
      "name": "Chen-Wei Wang"
    },
    {
      "name": "Diego López-Cámara"
    },
    {
      "name": "Daniel A Perley"
    },
    {
      "name": "Aleksandra Bochenek"
    },
    {
      "name": "Simone Dichiara"
    },
    {
      "name": "Enrique Moreno Méndez"
    },
    {
      "name": "Nathaniel R Butler"
    },
    {
      "name": "Benjamin Schneider"
    },
    {
      "name": "Jean-Luc Atteia"
    },
    {
      "name": "Stéphane Basa"
    },
    {
      "name": "William H Lee"
    },
    {
      "name": "Dalya Akl"
    },
    {
      "name": "Sarah Antier"
    },
    {
      "name": "Alexis Coleiro"
    },
    {
      "name": "James Delaunay"
    },
    {
      "name": "Damien Dornic"
    },
    {
      "name": "Jean-Grégoire Ducoin"
    },
    {
      "name": "Francis Fortin"
    },
    {
      "name": "Dmitry Frederiks"
    },
    {
      "name": "Leonardo García-García"
    },
    {
      "name": "Noémie Globus"
    },
    {
      "name": "Olivier Godet"
    },
    {
      "name": "Jamie Kennea"
    },
    {
      "name": "Gianluca Lombardi"
    },
    {
      "name": "Alexandra L Lysenko"
    },
    {
      "name": "Francesco Magnani"
    },
    {
      "name": "Tyler Parsotan"
    },
    {
      "name": "Margarita Pereyra"
    },
    {
      "name": "Anna Ridnaia"
    },
    {
      "name": "Samuele Ronchini"
    },
    {
      "name": "Fredd Sánchez-Álvarez"
    },
    {
      "name": "Dmitry Svinkin"
    },
    {
      "name": "Anastasia Tsvetkova"
    },
    {
      "name": "Mikhail Ulanov"
    },
    {
      "name": "Peter Veres"
    },
    {
      "name": "Hui Yang"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7chkz6bk5sw1f.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.27127",
  "fulltext_url": null,
  "id": "7chkz6bk5sw1f",
  "issns": [],
  "landing_url": "https://hal.science/hal-05785800v1",
  "language": "en",
  "licence": "CC-BY-NC-SA-4.0",
  "licence_label": "CC BY-NC-SA 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by-nc-sa/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
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      "astro-ph.HE"
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    [
      "hal",
      "0.phys"
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    [
      "hal",
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    [
      "openalex",
      "3103|Gamma-ray bursts and supernovae"
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  "openalex": "W7214206963",
  "pdf_url": "https://arxiv.org/pdf/2609.27127",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-22",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/7chkz6bk5sw1f.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:50Z",
      "native_id": "hal-05785800",
      "source": "hal",
      "url": "https://hal.science/hal-05785800v1"
    },
    {
      "first_seen": "2026-10-30T12:23:56Z",
      "native_id": "2609.27127",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.27127"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    },
    {
      "field": "physics",
      "origin": "hal:0.phys",
      "subfield": "general"
    }
  ],
  "title": "EP260119a: A High-Redshift Gamma-Ray Quiet Fast X-ray Transient Probing a Potentially Hidden Population of Relativistic Explosions",
  "title_text": "EP260119a: A High-Redshift Gamma-Ray Quiet Fast X-ray Transient Probing a Potentially Hidden Population of Relativistic Explosions",
  "type": "preprint",
  "updated_at": "2026-10-30T12:23:56Z",
  "url": "https://research.draconitic.com/paper/7chkz6bk5sw1f",
  "venue": "HAL",
  "versions": []
}