快速射电暴来自受激上散射。I. 磁星极区火球
Fast Radio Bursts from Induced Upscattering. I. Magnetar Polar Fireballs
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中文总结 AI 辅助
本文提出磁星极区火球中受激康普顿上散射产生快速射电暴的模型，推导光度与带宽关系，解释银河系FRB 20200428并预测重复暴趋势。
中文摘要 AI 辅助
快速射电暴（FRBs）的极高亮温度要求一种相干过程，将磁星暴发能量转化为毫秒射电辐射。我们提出，FRBs 可以在磁星磁层内通过相对论火球外流中的受激（受迫）上散射产生。本文聚焦于从磁星极区发射的电子-正电子火球中的受激康普顿上散射。X射线暴辐射将极区火球外流加速至洛伦兹因子 Γ~10--10^3。低频种子波（如快磁声波或阿尔文波）从侧面或逆向外流进入外流，经历受激散射，并被相对论整体运动从 ν0~10kHz 洛伦兹提升至 ν_obs~Γ^2ν0~GHz。结合极区火球动力学与受激散射不稳定性的线性增长和非线性饱和，我们推导出 FRB 各向同性光度 L_FRB^iso 和分数谱带宽 Δν/ν_c。通过考虑可能的电子-正电子对密度和温度范围，我们发现该极区通道可以解释银河系 FRB 20200428 的光度，并达到与最亮河外 FRB 相当的光度。如果对载荷区域窄于相对论聚束角 1/Γ，该模型还产生窄谱，并预测 L_FRB^iso ∝ (Δν/ν_c)^2，这一趋势与重复 FRB 的观测一致。因此，受激上散射模型通过基于等离子体物理的相干发射过程将磁星 X 射线暴与 FRBs 联系起来，并做出可观测检验的预测。
英文摘要
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.
发表机构
- Center for Gravitational Physics and Quantum Information, Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所引力波与量子信息研究中心）
- The Hong Kong Institute for Astronomy and Astrophysics, The University of Hong Kong（香港大学香港天文及天体物理研究所）
- Department of Physics, The University of Hong Kong（香港大学物理学系）
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