{
  "abstract": "The extreme brightness temperatures of fast radio bursts (FRBs) demand a coherent process that converts magnetar burst energy into millisecond radio emission. We propose that FRBs can be produced within magnetar magnetospheres by induced (stimulated) upscattering in a relativistic fireball outflow. In this paper, we focus on induced Compton upscattering in an electron--positron fireball launched from the polar region of a magnetar. Radiation from the X-ray burst accelerates the polar fireball outflow to Lorentz factors of $Γ\\sim10$--$10^3$. Low-frequency seed waves, such as fast magnetosonic or Alfvén waves, entering the outflow from the side or against its motion undergo induced scattering and are Lorentz-boosted by the relativistic bulk motion from $ν_0\\sim10\\mathrm{kHz}$ to $ν_{\\rm obs}\\simΓ^2ν_0\\sim\\mathrm{GHz}$. Combining the polar fireball dynamics with the linear growth and nonlinear saturation of the induced scattering instability, we derive the FRB luminosity $L_{\\rm FRB}^{\\rm iso}$ and fractional spectral bandwidth $Δν/ν_{\\rm c}$. By considering the possible range of pair densities and temperatures, we find that this polar channel can account for the luminosity of Galactic FRB~20200428 and reach luminosities comparable to those of the brightest extragalactic FRBs. If the pair-loaded region is narrower than the relativistic beaming angle $1/Γ$, the model also produces a narrow spectrum and predicts $L_{\\rm FRB}^{\\rm iso}\\propto(Δν/ν_{\\rm c})^2$, a trend consistent with observations of repeating FRBs. The induced upscattering model thus connects magnetar X-ray bursts to FRBs through a coherent emission process grounded in plasma physics and makes observationally testable predictions.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.36114",
  "author_total": 3,
  "authors": [
    {
      "name": "Rei Nishiura"
    },
    {
      "name": "Kunihito Ioka"
    },
    {
      "name": "Bing Zhang"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fafkveceg1p1e.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.36114",
  "fulltext_url": null,
  "id": "fafkveceg1p1e",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.36114",
  "language": null,
  "licence": "CC0-1.0",
  "licence_label": "CC0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/publicdomain/zero/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "astro-ph.HE"
    ],
    [
      "arxiv",
      "physics.plasm-ph"
    ],
    [
      "openalex",
      "3103|Gamma-ray bursts and supernovae"
    ]
  ],
  "openalex": "W7214983761",
  "pdf_url": "https://arxiv.org/pdf/2609.36114",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-28",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/fafkveceg1p1e.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:25:31Z",
      "native_id": "2609.36114",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.36114"
    }
  ],
  "subjects": [
    {
      "field": "astronomy",
      "origin": "arxiv:astro-ph.HE",
      "subfield": "high-energy-astrophysics"
    },
    {
      "field": "physics",
      "origin": "arxiv:physics.plasm-ph",
      "subfield": "plasma"
    }
  ],
  "title": "Fast Radio Bursts from Induced Upscattering. I. Magnetar Polar Fireballs",
  "title_text": "Fast Radio Bursts from Induced Upscattering. I. Magnetar Polar Fireballs",
  "type": "preprint",
  "updated_at": "2026-10-30T12:25:31Z",
  "url": "https://research.draconitic.com/paper/fafkveceg1p1e",
  "venue": "arXiv",
  "versions": []
}