{
  "abstract": "Gravitational waves can be gravitationally lensed by massive objects along their path. Depending on the lens mass and the lens–source geometry, this can lead to the observation of a single distorted signal, multiple repeated events, or a mixture of both. We present the results for gravitational-wave lensing searches on the data from the first part of the fourth LIGO–Virgo–KAGRA observing run (O4a). We search for strongly lensed events in the newly acquired data by (1) searching for an overall phase shift present in an image formed at a saddle point of the lens potential, (2) looking for pairs of detected candidates with consistent frequency evolution, and (3) identifying subthreshold counterpart candidates to the detected signals. Beyond strong lensing, we also look for lensing-induced distortions in all detected signals using an isolated point-mass model. We do not find evidence for strongly lensed gravitational-wave signals and use this result to constrain the rate of detectable strongly lensed events and the merger rate density of binary black holes at high redshift. In the search for single distorted lensed signals, we find one outlier: GW231123_135430, for which we report more detailed investigations. While this event is interesting, the associated waveform uncertainties make its interpretation complicated, and future observations of the populations of binary black holes and of gravitational lenses will help determine the probability that this event could be lensed.",
  "abstract_shown": true,
  "affiliations": [
    "Max Planck Institute for Gravitational Physics (Albert Einstein Institute)",
    "LIGO Hanford Observatory",
    "Dipartimento di Farmacia",
    "INFN",
    "University of Warwick",
    "OzGrav",
    "The Pennsylvania State University",
    "Leibniz Universität Hannover",
    "University of Wisconsin-Milwaukee",
    "LIGO Laboratory",
    "Louisiana State University",
    "Tata Institute of Fundamental Research",
    "Centre de Physique Théorique",
    "Université catholique de Louvain",
    "Queen Mary University of London",
    "University of California",
    "University of Minnesota",
    "Instituto Nacional de Pesquisas Espaciais",
    "Université Paris Cité",
    "Università di Roma Tor Vergata",
    "Universiteit Antwerpen",
    "International Centre for Theoretical Sciences",
    "Gravitational Wave Science Project",
    "Advanced Technology Center",
    "Theoretisch-Physikalisches Institut",
    "INFN Sezione di Torino",
    "Dipartimento di Fisica",
    "Univ. Savoie Mont Blanc",
    "Università di Napoli “Federico II”",
    "Cardiff University",
    "Maastricht University",
    "Nikhef",
    "Università di Roma “La Sapienza”",
    "Aix Marseille Univ",
    "Université Paris-Saclay",
    "University of Tokyo",
    "Institut de Física d’Altes Energies (IFAE)",
    "Gran Sasso Science Institute (GSSI)",
    "University of Florida",
    "Dipartimento di Scienze Matematiche"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 1772,
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      ],
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      ],
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      "name": "F. Acernese"
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      "name": "K. Ackley",
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      ],
      "name": "C. Adamcewicz",
      "orcid": "0000-0001-5525-6255"
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      "orcid": "0009-0004-2101-5428"
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      "name": "W. Amar"
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      "name": "O. Amarasinghe"
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      "name": "A. Amato",
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      "name": "C. Amra"
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      "name": "A. Ananyeva"
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      "name": "S. B. Anderson",
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      "name": "W. G. Anderson",
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      ],
      "name": "J. Anglin"
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      "name": "S. Ansoldi",
      "orcid": "0000-0002-5613-7693"
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      "name": "J. M. Antelis",
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      "name": "S. Antier",
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    },
    {
      "name": "M. Aoumi"
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      "affs": [
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      "name": "E. Z. Appavuravther"
    },
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      "name": "S. Appert"
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      "name": "S. K. Apple",
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      "name": "M. Arca Sedda",
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      "name": "J. S. Areeda",
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      "name": "S. Armstrong"
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      "name": "N. Arnaud",
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  "bibtex": "https://research.draconitic.com/paper/593k2tkk5ty8r.bib",
  "cited_by": 0,
  "doi": "10.3847/1538-4357/ae9744",
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  "id": "593k2tkk5ty8r",
  "issns": [
    "1538-4357",
    "0004-637X"
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  "landing_url": "https://iopscience.iop.org/article/10.3847/1538-4357/ae9744",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
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  "pdf_url": "https://iopscience.iop.org/article/10.3847/1538-4357/ae9744/pdf",
  "pmcid": null,
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  "published": "2026-11-05",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/593k2tkk5ty8r.ris",
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  "subjects": [
    {
      "field": "astronomy",
      "origin": "journal-openalex:3103|Stellar, planetary, and galactic studies",
      "subfield": "stellar"
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  ],
  "title": "GWTC-4.0: Searches for Gravitational-wave Lensing Signatures",
  "title_text": "GWTC-4.0: Searches for Gravitational-wave Lensing Signatures",
  "type": "peer-reviewed",
  "updated_at": "2026-11-08T00:21:13Z",
  "url": "https://research.draconitic.com/paper/593k2tkk5ty8r",
  "venue": "The Astrophysical Journal",
  "versions": []
}