Self-modulation of fast radio bursts
Self-modulation of fast radio bursts
复制标题
DOI：
10.1093/mnras/staa3248
复制
发表时间：
2020-10
影响因子：
4.8
通讯作者：
E. Sobacchi;Y. Lyubarsky;A. Beloborodov;L. Sironi
中科院分区：
文献类型：
--
作者：
E. Sobacchi;Y. Lyubarsky;A. Beloborodov;L. Sironi
快速射电爆发（FRB）是一种极端的天体物理现象，它进入了非线性光学的领域，这是激光物理学的一个发展领域。经典的非线性效应是自调制。我们研究的传播FRB通过环暴环境中使用的理想化设置的单色线极化GHz波传播通过一个均匀的等离子体板的密度$N$在距离$R$从源。我们发现，如果板位于一个临界半径$R_{\rm crit}\sim 10^{17}（N/10 ^{2 {\rm\; cm}^{-3}）（L/10^{42}{\rm\; s}^{-1}）{\rm\; cm}$，其中$L$是FRB亮度的各向同性等效物，则会发生自调制。自调制将脉冲串分解成横向于径向的薄煎饼。当$R\lesssim R_{\rm crit}$时，煎饼的横向尺寸小于菲涅耳尺度。当爆发离开平板时，薄饼被强烈衍射，薄饼之间的干涉产生了对观测到的强度的频率调制，其带宽为亚GHz。当$R\sim R_{\rm crit}$时，煎饼的横向尺寸变得与菲涅耳尺度相当，并且衍射的影响较弱。观察到的强度在十微秒的时间尺度上调制，这对应于煎饼的径向宽度。我们的研究结果表明，自调制可能会导致在FRB中观察到的时间和频率结构。
Fast Radio Bursts (FRBs) are extreme astrophysical phenomena entering the realm of non-linear optics, a field developed in laser physics. A classical non-linear effect is self-modulation. We examine the propagation of FRBs through the circumburst environment using the idealised setup of a monochromatic linearly-polarised GHz wave propagating through a uniform plasma slab of density $N$ at distance $R$ from the source. We find that self-modulation occurs if the slab is located within a critical radius $R_{\rm crit}\sim 10^{17}(N/10^2{\rm\; cm}^{-3})(L/10^{42}{\rm\; erg\; s}^{-1}){\rm\; cm}$, where $L$ is the isotropic equivalent of the FRB luminosity. Self-modulation breaks the burst into pancakes transverse to the radial direction. When $R\lesssim R_{\rm crit}$, the transverse size of the pancakes is smaller than the Fresnel scale. The pancakes are strongly diffracted as the burst exits the slab, and interference between the pancakes produces a frequency modulation of the observed intensity with a sub-GHz bandwidth. When $R\sim R_{\rm crit}$, the transverse size of the pancakes becomes comparable with the Fresnel scale, and the effect of diffraction is weaker. The observed intensity is modulated on a timescale of ten microseconds, which corresponds to the radial width of the pancakes. Our results suggest that self-modulation may cause the temporal and frequency structure observed in FRBs.