{
  "abstract": "Unresolved millimeter (mm) emission is observed in radio-quiet (RQ) Active Galactic Nuclei (AGN), but its physical origin remains debated. Self-absorbed synchrotron emission from the compact X-ray corona is one of the leading candidates. Previous support for this coronal synchrotron origin has mainly been based on variability and spectral indices in a few RQ AGN, with a lack of (quasi-)simultaneous broadband data for larger samples. We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of nine nearby ($z \\sim 0.008-0.064$) RQ AGN, obtained quasi-simultaneously at 100, 145, and 233 GHz. Based on power-law fits to the spectral energy distributions, we measure millimeter spectral indices ranging from $-0.05^{+0.09}_{-0.09}$ to $0.88^{+0.12}_{-0.11}$. Furthermore, across two 100 GHz observing epochs per source, separated by $4-11$ days, we detect flux density variability of $30-56$% (>$3σ$ significance level) in three out of nine sources. Spectral slopes alone are insufficient to constrain the origin of the millimeter emission; however, the observed short-timescale variability and inferred brightness temperature values are consistent with a non-thermal emission mechanism arising from a compact emitting region with a size of $R_{\\rm mm}< 10^3 - 10^4 R_{\\rm g}$, such as the corona or a compact jet. Furthermore, we find a clear correlation between the 100/233 GHz and X-ray flux in our sample, and establish a new linear correlation between 145 GHz and X-ray emission.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2610.30286",
  "author_total": 11,
  "authors": [
    {
      "name": "Sophie M. Venselaar"
    },
    {
      "name": "Claudio Ricci"
    },
    {
      "name": "Yoshiyuki Inoue"
    },
    {
      "name": "Chin-Shin Chang"
    },
    {
      "name": "Akihiro Doi"
    },
    {
      "name": "Noemi Barnier"
    },
    {
      "name": "Taiki Kawamuro"
    },
    {
      "name": "Susanne Aalto"
    },
    {
      "name": "Momoka Hamamoto"
    },
    {
      "name": "Elena Shablovinskaya"
    },
    {
      "name": "Ezequiel Treister"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7ze1pdkrfqk6d.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2610.30286",
  "fulltext_url": null,
  "id": "7ze1pdkrfqk6d",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2610.30286",
  "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.GA"
    ],
    [
      "arxiv",
      "astro-ph.HE"
    ],
    [
      "openalex",
      "3103|Astrophysical Phenomena and Observations"
    ]
  ],
  "openalex": "W7223386443",
  "pdf_url": "https://arxiv.org/pdf/2610.30286",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-21",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/7ze1pdkrfqk6d.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:34:34Z",
      "native_id": "2610.30286",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2610.30286"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.GA",
      "subfield": "galaxies"
    },
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    }
  ],
  "title": "Nuclear Millimeter Continuum Emission in Radio-Quiet Active Galactic Nuclei: an ALMA Spectral and Variability Study",
  "title_text": "Nuclear Millimeter Continuum Emission in Radio-Quiet Active Galactic Nuclei: an ALMA Spectral and Variability Study",
  "type": "preprint",
  "updated_at": "2026-10-30T12:34:34Z",
  "url": "https://research.draconitic.com/paper/7ze1pdkrfqk6d",
  "venue": "arXiv",
  "versions": []
}