Filamentation of fast radio bursts in magnetar winds
Filamentation of fast radio bursts in magnetar winds
复制标题
磁星风中快速射电暴的丝状结构
DOI：
10.1093/mnras/stac251
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发表时间：
2022
影响因子：
4.8
通讯作者：
Sironi, Lorenzo
中科院分区：
文献类型：
--
作者：
Sobacchi, Emanuele;Lyubarsky, Yuri;Beloborodov, Andrei M.;Sironi, Lorenzo
磁星是快速射电暴（FRB）最有希望的起源。通过磁星风传播的强无线电波会受到非线性效应的影响，包括调制/丝状不稳定性。我们推导了在磁控对等离子体中传播的强波调制的色散关系，重点关注无量纲强度参数 a0≲ 1，并讨论了对快速射电暴的影响。由于不稳定性的影响，FRB 辐射强度会形成垂直于风磁场方向的片状。当快速射电暴锋面扩展到不稳定性结束的半径之外时，辐射片会因衍射而散射。 FRB 散射时间尺度取决于磁星风的特性。在冷风中，典型的散射时标在频率处为 τsc∼s–ms。散射时间尺度在低频处增加，缩放比例为 τsc∝ν−2。 FRB 181112 最亮脉冲的频率相关展宽与这种缩放比例一致。根据脉冲的散射时间尺度，可以估计风的洛伦兹因子大于几十。在暖风中，散射时间尺度可以接近。然后散射产生具有大带宽的观测强度的频率调制。在快速射电暴中观察到的宽带频率调制可能是由于温暖的磁星风中的散射造成的。
Magnetars are the most promising progenitors of fast radio bursts (FRBs). Strong radio waves propagating through the magnetar wind are subject to non-linear effects, including modulation/filamentation instabilities. We derive the dispersion relation for modulations of strong waves propagating in magnetically dominated pair plasmas focusing on dimensionless strength parametersa0≲ 1, and discuss implications for FRBs. As an effect of the instability, the FRB-radiation intensity develops sheets perpendicular to the direction of the wind magnetic field. When the FRB front expands outside the radius where the instability ends, the radiation sheets are scattered due to diffraction. The FRB-scattering time-scale depends on the properties of the magnetar wind. In a cold wind, the typical scattering time-scale is τsc∼s–ms at the frequency. The scattering time-scale increases at low frequencies, with the scaling τsc∝ν−2. The frequency-dependent broadening of the brightest pulse of FRB 181112 is consistent with this scaling. From the scattering time-scale of the pulse, one can estimate that the wind Lorentz factor is larger than a few tens. In a warm wind, the scattering time-scale can approach. Then scattering produces a frequency modulation of the observed intensity with a large bandwidth,. Broad-band frequency modulations observed in FRBs could be due to scattering in a warm magnetar wind.