Interaction of Strong X-mode Waves with Magnetized Pair Plasmas

The interaction of strong ($a_0>1$), superluminal X-mode electromagnetic waves with magnetized pair plasma falls into two regimes set by $\varepsilon_{\rm B}\equiv a_0ω_{\rm B}/ω_0$, the ratio of the wave strength parameter to its frequency, in units of cyclotron frequency. For $\varepsilon_{\rm B}<1$ the wave propagates until induced scattering disrupts it. Using analytical theory and kinetic simulations, we show that the background magnetic field introduces a restoring frequency $Ω_{\rm B}$ to scattering; when $Ω_{\rm B}$ exceeds the scattering rate, the unattenuated length grows from $\simeq\varepsilon_{\rm p}^{-2/3}$ to $\simeq\varepsilon_{\rm B}^{1/2}/\varepsilon_{\rm p}$ wavelengths ($\varepsilon_{\rm p}\equiv a_0ω_{\rm p}/ω_0$; $ω_{\rm p}$ is the plasma frequency). When $a_0^2>\varepsilon_{\rm B}>1$, the plasma current is nonlinear, and the wave is damped while riding a motional electric field, so one half-cycle appears attenuated. This framework has implications for the duration of fast radio bursts and whether they can escape their surroundings.