{
  "abstract": "Magnetic effects are thought to dominate the formation of BL Lac object jets, but the role and influence of large-scale magnetic fields within the jets remains incompletely understood. We utilize a one-zone synchrotron-self-Compton (SSC) model with broken-power-law electron injection to reproduce multiwavelength spectral energy distributions (SEDs) of the high-synchrotron-peaked BL Lac object Mrk 421 for 73 activity states, constraining six key physical parameters. We investigate the correlation between magnetic-field strength B and emission-region size R and estimate the powers of relativistic electrons, cold protons, magnetic fields, and total jet power. We find a significant anticorrelation log B = ( − 0.93 ± 0.05 ) log R + ( 14.22 ± 0.83 ) . The derived slope close to −1 is compatible with theoretical expectations for a toroidal magnetic geometry, though parameter couplings inherent to the leptonic model cannot be fully excluded. Markov Chain Monte Carlo (MCMC) posterior analyses demonstrate that this B – R scaling is not merely an artefact of intra-epoch parameter degeneracy. On emission-region scales the jet is particle-kinetic-energy dominated; distinct electron-acceleration mechanisms (shocks, magnetic reconnection) operate across different activity states, and the conventional Poynting-flux-dominated scenario cannot account for the observed radiative power.",
  "abstract_shown": true,
  "affiliations": [
    "Yunnan University",
    "Yunnan Normal University"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 3,
  "authors": [
    {
      "affs": [
        0,
        1
      ],
      "name": "Y. B. Xu",
      "orcid": "0009-0006-1947-9121"
    },
    {
      "affs": [
        1
      ],
      "name": "Y. G. Zheng",
      "orcid": "0000-0003-0170-9065"
    },
    {
      "affs": [
        0
      ],
      "name": "L. Zhang",
      "orcid": "0000-0002-5880-8497"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/ec5h8e9yex3hv.bib",
  "cited_by": 0,
  "doi": "10.3847/1538-4357/aea615",
  "fulltext_url": null,
  "id": "ec5h8e9yex3hv",
  "issns": [
    "1538-4357",
    "0004-637X"
  ],
  "landing_url": "https://iopscience.iop.org/article/10.3847/1538-4357/aea615",
  "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"
    ]
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  "pdf_url": "https://iopscience.iop.org/article/10.3847/1538-4357/aea615/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-11-06",
  "publisher": "American Astronomical Society",
  "ris": "https://research.draconitic.com/paper/ec5h8e9yex3hv.ris",
  "sources": [
    {
      "first_seen": "2026-11-06T06:20:02Z",
      "native_id": "10.3847/1538-4357/aea615",
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      "url": "https://iopscience.iop.org/article/10.3847/1538-4357/aea615"
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  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "journal-openalex:3103|Stellar, planetary, and galactic studies",
      "subfield": "stellar"
    }
  ],
  "title": "The Relation between Magnetic-field Intensity and Size of the Emission Region in the High-synchrotron-peaked BL Lacertae Object Mrk 421",
  "title_text": "The Relation between Magnetic-field Intensity and Size of the Emission Region in the High-synchrotron-peaked BL Lacertae Object Mrk 421",
  "type": "peer-reviewed",
  "updated_at": "2026-11-08T00:21:13Z",
  "url": "https://research.draconitic.com/paper/ec5h8e9yex3hv",
  "venue": "The Astrophysical Journal",
  "versions": []
}