The moving mirror model for fast radio bursts

Abstract

ABSTRACT Recent observations of coherent radiation from the Crab pulsar suggest the emission is driven by an ultrarelativistic (γ ∼ 104), cold plasma flow. A relativistically expanding plasma shell can compress the ambient magnetic field, like a moving mirror, and thus produce coherent radiation whose wavelength is shorter than that of the ambient medium by γ2. This mechanism has been previously studied in the context of radio loud supernova explosions. In this work, we propose that a similar mechanism drives the coherent emission in fast radio bursts. The high Lorenz factors dramatically lower the implied energy and magnetic field requirements, allowing the spin-down energy of regular (or even recycled), fast spinning pulsars, rather than slow spinning magnetars, to explain FRBs. We show that this model can explain the frequency and the time evolution of observed FRBs, as well as their duration, energetics, and absence of panchromatic counterparts. We also predict that the peak frequency of subpulses decline with observation time as $\omega _{\rm obs} \propto t_{\rm obs}^{-1/2}$. Unfortunately, with current capabilities it is not possible to constrain the shape of the curve ωobs(tobs). Finally, we find that a variation of this model can explain weaker radio transients, such as the one observed from a galactic magnetar. In this variant, the shock wave produces low-frequency photons that are then Compton scattered to the GHz range.