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Register a new userScattering of ultrastrong electromagnetic waves by magnetized particles
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Added by
Andrei M. Beloborodov
Publication date
2021
fields
Physics
and research's language is
English
Authors
Andrei M. Beloborodov
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Observations of powerful radio waves from neutron star magnetospheres raise the question of how strong waves interact with particles in a strong background magnetic field $B_{bg}$. This problem is examined by solving the particle motion in the wave. Remarkably, waves with amplitudes $E_0>B_{bg}$ pump particle energy via repeating resonance events, quickly reaching the radiation reaction limit. As a result, the wave is scattered with a huge cross section. This fact has great implications for models of fast radio bursts and magnetars. Particles accelerated in the wave emit gamma-rays, which can trigger an $e^pm$ avalanche and, instead of silent escape, the wave will produce X-ray fireworks.
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The review is devoted to a discussion of new (and often unexpected) aspects of the old problem of elastic light scattering by small metal particles, whose size is comparable to or smaller than the thickness of the skin layer. The main focus is put on elucidating the physical grounds for these new aspects. It is shown that, in many practically important cases, the scattering of light by such particles, despite their smallness, may have almost nothing in common with the Rayleigh one. The so-called, anomalous scattering and absorption, as well as Fano resonances, including unconventional (associated with the excitation of longitudinal electromagnetic oscillations) and directional Fano resonances, observed only in a small solid angle, are discussed in detail. The review contains a Mathematical Supplement, which includes a summary of the main results of the Mie theory and a discussion of some general properties of the scattering coefficients. In addition to purely academic interest, the phenomena considered in this review can find wide applications in biology, medicine, pharmacology, genetic engineering, imaging of ultra-small objects, ultra-high-resolution spectroscopy, information transmission, recording, and processing, and many other applications and technologies. The reported study was funded by RFBR, project number 19-11-00001 and the project of the Russian Science Foundation No. 19-72-30012, within the framework of which all the original calculations given in this publication were performed.
Relativistic magnetized shocks are a natural source of coherent emission, offering a plausible radiative mechanism for Fast Radio Bursts (FRBs). We present first-principles 3D simulations that provide essential information for the FRB models based on shocks: the emission efficiency, spectrum, and polarization. The simulated shock propagates in an $e^pm$ plasma with magnetization $sigma>1$. The measured fraction of shock energy converted to coherent radiation is $simeq 10^{-3} , sigma^{-1}$, and the energy-carrying wavenumber of the wave spectrum is $simeq 4 ,omega_{rm c}/c$, where $omega_{rm c}$ is the upstream gyrofrequency. The ratio of the O-mode and X-mode energy fluxes emitted by the shock is $simeq 0.4,sigma^{-1}$. The dominance of the X-mode at $sigmagg 1$ is particularly strong, approaching 100% in the spectral band around $2,omega_{rm c}$. We also provide a detailed description of the emission mechanism for both X- and O-modes.
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