{
  "abstract": "Circumnuclear structures in active galactic nuclei (AGN) respond to accretion variability over different spatial and temporal scales, but whether compact narrow-line gas responds on decade timescales has not been systematically established. We use repeat Sloan Digital Sky Survey and Dark Energy Spectroscopic Instrument spectroscopy of 473 variability-selected galactic nuclei with evidence for recent nuclear brightening. We identify 19 sources whose narrow [O III ] λ 5007 flux increased by more than a factor of 2 over rest-frame baselines of 12.0–20.4 yr, which we term narrow-line ionization echoes (NIEs). In equal-weight stacked spectra, [O III ] increased by 229% ± 22%, while lower-ionization lines remained nearly unchanged or declined, indicating an ionization-dependent response rather than uniform spectral rescaling. The NIE hosts also moved coherently toward higher excitation in optical diagnostic diagrams, with mean increases of 0.46 ± 0.18 dex in log ( [ O III ] / H β ) and 0.58 ± 0.13 dex in log ( [ O III ] / [ O II ] ) . Photoionization models reproduce this evolution with a higher ionization parameter and a harder AGN-like ionizing spectrum at fixed gas abundance. For 13 sources with well-defined mid-infrared (MIR) outbursts, the integrated W1+W2 excess energy correlates strongly with the absolute [O III ] luminosity change ( r = 0.87), linking the dust and narrow-line responses to the same nuclear event. The MIR timescale and spectroscopic baseline constrain the variable [O III ]-emitting gas to characteristic scales of 1.5–5.2 pc. Compact narrow-line gas therefore appears to form an intermediate, decade-scale response layer between the infrared dust echo and the long-lived extended narrow-line region.",
  "abstract_shown": true,
  "affiliations": [
    "Chinese Academy of Sciences",
    "Durham University",
    "Nanjing University",
    "University of Michigan",
    "European Southern Observatory",
    "International Gemini Observatory/NSF NOIRLab",
    "Peking University",
    "Nanjing Normal University",
    "Università di Firenze",
    "INAF–Osservatorio Astrofisico di Arcetri",
    "University of Chinese Academy of Sciences"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 19,
  "authors": [
    {
      "affs": [
        0,
        1
      ],
      "name": "Wei-Jian Guo",
      "orcid": "0000-0001-9457-0589"
    },
    {
      "affs": [
        0
      ],
      "name": "Shuo Zhai",
      "orcid": "0009-0005-4152-2088"
    },
    {
      "affs": [
        0
      ],
      "name": "Chen Hu"
    },
    {
      "affs": [
        1
      ],
      "name": "David M. Alexander",
      "orcid": "0000-0002-5896-6313"
    },
    {
      "affs": [
        2
      ],
      "name": "Bin Luo",
      "orcid": "0000-0002-9036-0063"
    },
    {
      "affs": [
        0
      ],
      "name": "Pu Du",
      "orcid": "0000-0002-5830-3544"
    },
    {
      "affs": [
        1
      ],
      "name": "Matthew J. Temple",
      "orcid": "0000-0001-8433-550X"
    },
    {
      "affs": [
        1
      ],
      "name": "Leah K. Morabito",
      "orcid": "0000-0003-0487-6651"
    },
    {
      "affs": [
        3
      ],
      "name": "Feige Wang",
      "orcid": "0000-0002-7633-431X"
    },
    {
      "affs": [
        3
      ],
      "name": "Jinyi Yang",
      "orcid": "0000-0001-5287-4242"
    },
    {
      "affs": [
        4
      ],
      "name": "Victoria A. Fawcett",
      "orcid": "0000-0003-1251-532X"
    },
    {
      "affs": [
        5
      ],
      "name": "Swayamtrupta Panda",
      "orcid": "0000-0002-5854-7426"
    },
    {
      "affs": [
        1
      ],
      "name": "Claire L. Greenwell",
      "orcid": "0000-0002-7719-5809"
    },
    {
      "affs": [
        0
      ],
      "name": "Yan-Rong Li",
      "orcid": "0000-0001-5841-9179"
    },
    {
      "affs": [
        0
      ],
      "name": "Cheng Cheng",
      "orcid": "0000-0003-0202-0534"
    },
    {
      "affs": [
        6
      ],
      "name": "Shengxiu Sun",
      "orcid": "0000-0002-1234-552X"
    },
    {
      "affs": [
        7
      ],
      "name": "Zhi-Qiang Chen",
      "orcid": "0009-0008-3338-393X"
    },
    {
      "affs": [
        8,
        9
      ],
      "name": "Alessandro Marconi",
      "orcid": "0000-0002-9889-4238"
    },
    {
      "affs": [
        0,
        10
      ],
      "name": "Jian-Min Wang",
      "orcid": "0000-0001-9449-9268"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/4vfe6xswhy5j7.bib",
  "cited_by": 0,
  "doi": "10.3847/1538-4357/aeae2b",
  "fulltext_url": null,
  "id": "4vfe6xswhy5j7",
  "issns": [
    "1538-4357",
    "0004-637X"
  ],
  "landing_url": "https://iopscience.iop.org/article/10.3847/1538-4357/aeae2b",
  "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/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "feed-journal",
      "astronomy/general"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://iopscience.iop.org/article/10.3847/1538-4357/aeae2b/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-04",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/4vfe6xswhy5j7.ris",
  "sources": [
    {
      "first_seen": "2026-11-04T18:20:26Z",
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    {
      "first_seen": "2026-11-05T00:20:44Z",
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  "subjects": [
    {
      "field": "astronomy",
      "origin": "journal-openalex:3103|Stellar, planetary, and galactic studies",
      "subfield": "stellar"
    }
  ],
  "title": "A Decade-scale Ionization Echo of Black Hole Accretion in Galactic Nuclei",
  "title_text": "A Decade-scale Ionization Echo of Black Hole Accretion in Galactic Nuclei",
  "type": "peer-reviewed",
  "updated_at": "2026-11-06T00:21:00Z",
  "url": "https://research.draconitic.com/paper/4vfe6xswhy5j7",
  "venue": "The Astrophysical Journal",
  "versions": []
}