paper

Constraints on the Engines of Fast Radio Bursts

arXiv:1911.05765 · doi:10.1093/mnras/staa1036

Abstract

We model the sample of fast radio bursts (FRB), including the newly discovered CHIME repeaters, using the synchrotron blast wave model of Metzger, Margalit & Sironi (2019). This model postulates that FRBs are precursor radiation from ultra-relativistic magnetized shocks generated as flare ejecta from a central engine collide with an effectively stationary external medium. Downward drifting of the burst frequency structure naturally arises from deceleration of the blast-wave. The data are consistent with FRBs being produced by flares of energy erg, where is the maser efficiency, and minimum bulk Lorentz factors , which generate the observed FRBs at shock radii cm. We infer upstream densities cm and radial profiles showing a range of slopes (which are seen to evolve between bursts), broadly consistent with the upstream medium being the inner edge of an ion-loaded shell released by a recent energetic flare. The burst timescales, energetics, rates, and external medium properties are consistent with repeating FRBs arising from young, hyper-active flaring magnetars, but the methodology presented is generally applicable to any central engine which injects energy impulsively into a dense magnetized medium. Uncertainties and variations of the model are discussed, including the effects of the strong electric field of the FRB wave (strength parameter ) on the upstream medium. One-dimensional particle-in-cell simulations of magnetized shocks into a pair plasma are presented which demonstrate that high maser efficiency can be preserved, even in the limit in which the FRB wave accelerates the upstream electrons to ultra-relativistic speeds.

MNRAS accepted version

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