{
  "abstract": "High-energy astrophysical neutrinos serve as crucial messengers for understanding hadronic acceleration processes and identifying the origins of cosmic rays, with blazars among the most promising neutrino sources. The KM3NeT experiment reported the detection of an ultrahigh-energy neutrino with an energy estimate of ∼220 PeV, the most energetic yet observed. The neutrino arrival direction has a 99% confidence region of 3° radius centered at R.A. 94 . ° 3, decl. −7 . ° 8 (J2000). In this work, 17 candidate blazars located within this region are identified. Comprehensive new observations and archival data analysis for these sources are presented. The study provides a complete multiwavelength coverage across radio, optical, X-ray, and gamma-ray bands, including proprietary data and dedicated follow-up observations. This study highlights flaring behavior in several candidate counterparts. One object exhibits a radio flare coinciding with the neutrino arrival time, with a pre-trial chance probability of 0.26%. Only for this object, the chance probability could be quantified in a robust way. Another candidate displays a rising trend in X-ray flux in a 1 yr window around the neutrino arrival time, while a third undergoes a gamma-ray flare during the same period. Based on the observational findings presented here, while none of these candidates can conclusively be linked to the neutrino, the implications of a possible blazar origin for the KM3NeT event are discussed.",
  "abstract_shown": true,
  "affiliations": [
    "INFN",
    "Università di Firenze",
    "Université de Haute Alsace",
    "Université de Strasbourg",
    "IPHC - Institut Pluridisciplinaire Hubert Curien (23 rue Loess - BP 28 67037 Strasbourg Cedex - France)",
    "Université de Haute-Alsace (UHA) - Université de Haute-Alsace (UHA) Mulhouse - Colmar (2, rue des Frères Lumière F-68093 Mulhouse Cedex - France)",
    "Khalifa University of Science and Technology",
    "Aix Marseille Univ",
    "CPPM - Centre de Physique des Particules de Marseille (163, avenue de Luminy - Case 902 - 13288 Marseille cedex 09 - France)",
    "IFIC—Instituto de Física Corpuscular (CSIC—Universitat de València)",
    "Complesso Universitario di Monte S. Angelo",
    "Università di Napoli “Federico II,”",
    "Universitat Politècnica de Catalunya",
    "Nantes Université",
    "SUBATECH - Laboratoire de physique subatomique et des technologies associées (IMT Atlantique - Campus de Nantes - La Chantrerie - 4, rue Alfred Kastler - CS 20722 - 44307 NANTES Cedex 3 - France)",
    "Universitat Politècnica de València",
    "Université Paris Cité",
    "APC (UMR_7164) - AstroParticule et Cosmologie (APC - UMR 7164, Université Paris Diderot, 10 rue Alice Domon et Léonie Duquet, case postale 7020, F-75205 Paris Cedex 13 - France)",
    "Università di Genova",
    "LPC CAEN",
    "LPCC - Laboratoire de physique corpusculaire de Caen (ENSICAEN - 6, boulevard du Marechal Juin 14050 Caen Cedex - France)",
    "Comenius University in Bratislava",
    "Czech Technical University in Prague",
    "Università di Bologna",
    "Università degli Studi della Campania “Luigi Vanvitelli,”",
    "University of Hull",
    "Nikhef",
    "North-West University",
    "Université Badji Mokhtar",
    "University Mohammed V in Rabat",
    "Università di Salerno e INFN Gruppo Collegato di Salerno",
    "Institute of Space Science—INFLPR Subsidiary",
    "University of Amsterdam",
    "TNO",
    "Deutsches Elektronen-Synchrotron DESY",
    "Julius-Maximilians-Universität Würzburg",
    "Università La Sapienza",
    "Cadi Ayyad University",
    "University of the Witwatersrand"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 100,
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      "name": "A. Albert"
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      "name": "A. R. Alhebsi"
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      "name": "S. Alves Garre"
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      "name": "A. Ambrosone"
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      "name": "F. Ameli"
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      "name": "M. Andre"
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      "name": "L. Aphecetche"
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      "name": "S. Ardid"
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      "name": "Danilo Luigi Bonanno",
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  "doi": "10.3847/1538-3881/ae7a4e",
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    "0004-6256",
    "1538-3881"
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  "landing_url": "https://doi.org/10.3847/1538-3881/ae7a4e",
  "language": "en",
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  "licence_label": "CC BY 4.0",
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  "pdf_url": "https://iopscience.iop.org/article/10.3847/1538-3881/ae7a4e/pdf",
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  "published": "2026-08-05",
  "publisher": "Institute of Physics",
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  "title": "Characterizing Candidate Blazar Counterparts of the Ultra-high-energy Event KM3-230213A",
  "title_text": "Characterizing Candidate Blazar Counterparts of the Ultra-high-energy Event KM3-230213A",
  "type": "peer-reviewed",
  "updated_at": "2026-11-08T13:20:37Z",
  "url": "https://research.draconitic.com/paper/cn093es12qyfr",
  "venue": "The Astronomical Journal",
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