{
  "abstract": "While the connection of Fast X-ray Transients (FXTs) detected by Einstein Probe (EP) with Gamma-ray Bursts (GRBs) is increasingly compelling, most lack gamma-ray counterparts, leaving their relation to GRBs unclear. We performed a systematic search for gamma-ray counterparts to the 72 transients detected by EP in its first year, using targeted searches in Fermi/GBM and Fermi/LAT data, complemented by SVOM/GRM, SVOM/ECLAIRs, Swift/BAT and Konus-Wind. For the visible events without a gamma-ray counterpart, we derived simultaneous $3σ$ flux upper limits in the 10-1000 keV and the 0.1-1 GeV band. We find that 23 events (32%) have a gamma-ray counterpart (seven sub-threshold), while 49 events (68%) have none, despite most being visible. For events with a gamma-ray counterpart, the X-ray flux over the gamma-ray $T_{\\rm 90}$ is systematically higher than over the full X-ray duration, with flux ratios $1 \\lesssim F_{\\rm [10-1000\\,keV]}/F_{\\rm [0.5-4\\,keV]} \\lesssim 100$, suggesting that gamma-rays are preferentially detected during the brightest X-ray phases. For events without gamma-ray counterpart, the most stringent Fermi/GBM upper limits imply $E_{\\rm peak} \\lesssim 30$-100 keV and, for the 14 events with measured redshifts, $L_{\\rm iso}\\lesssim 10^{48}-9\\times10^{51}$ erg/s. If classical GRB correlations hold in this regime, these lower energetics imply lower bulk Lorentz factors ($Γ_0 \\lesssim 100$), as confirmed in a few cases by afterglow constraints. No significant GeV emission was detected by Fermi/LAT, yielding $1 \\lesssim F_{0.1-1\\,{\\rm GeV}}/F_{0.5-4\\,{\\rm keV}} \\lesssim 10$, placing the first constraints on a potential synchrotron self-Compton component for this new population. Although individual origins remain uncertain, many EP FXTs could be compatible with the GRB population, extending it toward lower $E_{\\rm peak}$, luminosities, and bulk Lorentz factors.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.28734",
  "author_total": 26,
  "authors": [
    {
      "name": "Maria Edvige Ravasio"
    },
    {
      "name": "Ansh Chopra"
    },
    {
      "name": "Peter G. Jonker"
    },
    {
      "name": "Qinyu Wu"
    },
    {
      "name": "Eric Burns"
    },
    {
      "name": "Biswajit Banerjee"
    },
    {
      "name": "Gor Oganesyan"
    },
    {
      "name": "Stefano Ascenzi"
    },
    {
      "name": "Jesse T. Palmerio"
    },
    {
      "name": "Frederic Daigne"
    },
    {
      "name": "Joshua Wood"
    },
    {
      "name": "Rachel Hamburg"
    },
    {
      "name": "Andrew J. Levan"
    },
    {
      "name": "Jonathan A. Quirola-Vasquez"
    },
    {
      "name": "Javier Sanchez-Sierras"
    },
    {
      "name": "Joyce N. D. van Dalen"
    },
    {
      "name": "Agnes P. C. van Hoof"
    },
    {
      "name": "Hui Sun"
    },
    {
      "name": "Weimin Yuan"
    },
    {
      "name": "Nikhil Sarin"
    },
    {
      "name": "Antonio Martin-Carrillo"
    },
    {
      "name": "Dylan Adrien"
    },
    {
      "name": "Ce Cai"
    },
    {
      "name": "YanQiu Zhang"
    },
    {
      "name": "Samuele Ronchini"
    },
    {
      "name": "Marica Branchesi"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/2kpndb26z0mem.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.28734",
  "fulltext_url": null,
  "id": "2kpndb26z0mem",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.28734",
  "language": null,
  "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": [
    [
      "arxiv",
      "astro-ph.HE"
    ],
    [
      "openalex",
      "3103|Gamma-ray bursts and supernovae"
    ]
  ],
  "openalex": "W7223196900",
  "pdf_url": "https://arxiv.org/pdf/2610.28734",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-20",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/2kpndb26z0mem.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:34:19Z",
      "native_id": "2610.28734",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.28734"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "The (missing) gamma-ray counterparts to EP events",
  "title_text": "The (missing) gamma-ray counterparts to EP events",
  "type": "preprint",
  "updated_at": "2026-10-30T12:34:19Z",
  "url": "https://research.draconitic.com/paper/2kpndb26z0mem",
  "venue": "arXiv",
  "versions": []
}