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PreprintCC0arXiv

Fast Radio Bursts from Induced Upscattering. I. Magnetar Polar Fireballs

  • Rei Nishiura
  • Kunihito Ioka
  • Bing Zhang
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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∼10--103. 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 ν0∼10kHz to νobs∼Γ2ν0∼GHz. Combining the polar fireball dynamics with the linear growth and nonlinear saturation of the induced scattering instability, we derive the FRB luminosity LFRBiso and fractional spectral bandwidth Δν/νc. 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 LFRBiso∝(Δν/νc)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.

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Cite

BibTeXRIS
BibTeX
@misc{nishiura2026fast,
  title = {{Fast Radio Bursts from Induced Upscattering. I. Magnetar Polar Fireballs}},
  author = {Rei Nishiura and Kunihito Ioka and Bing Zhang},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.36114},
  eprint = {2609.36114},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.36114},
  note = {CC0},
}
RIS
TY  - UNPB
TI  - Fast Radio Bursts from Induced Upscattering. I. Magnetar Polar Fireballs
AU  - Rei Nishiura
AU  - Kunihito Ioka
AU  - Bing Zhang
PY  - 2026
DA  - 2026/09/28
PB  - arXiv
DO  - 10.48550/arxiv.2609.36114
UR  - https://arxiv.org/abs/2609.36114
AB  - 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∼10--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∼10kHz to ν_obs∼Γ^2ν_0∼GHz. Combining the polar fireball dynamics with the linear growth and nonlinear saturation of the induced scattering instability, we derive the FRB luminosity L_FRB^iso and fractional spectral bandwidth Δν/ν_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_FRB^iso∝(Δν/ν_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.
ER  -