Escape of Fast Radio Bursts from magnetars' magnetospheres

TL;DR

This paper explores the physical processes affecting the production and escape of Fast Radio Bursts from magnetar magnetospheres, emphasizing the role of magnetic fields, radiative losses, and potential external perturbations.

Contribution

It provides a detailed analysis of dissipative mechanisms and conditions enabling FRB escape from magnetar magnetospheres, highlighting effects like ponderomotive acceleration and Landau-Pomeranchuk-Migdal suppression.

Findings

High magnetic fields are essential for FRB energetics and suppression of non-coherent losses.

Radiative losses are minimized by plasma acceleration and interference effects, allowing FRB escape.

External perturbations can dissipate FRB energy, producing detectable UV/X-ray signals.

Abstract

We discuss dissipative processes occurring during production and escape of Fast Radio Bursts (FRBs) from magnetars' magnetospheres, the presumed loci of FRBs. High magnetic fields are required in the emission region, both to account for the overall energetics of FRBs, and in order to suppress ``normal'' (non-coherent) radiative losses of radio emitting particles; this limits the emission radii to $\leq {\rm few} \times 10 R_{NS}$. Radiative losses by particles in the strong FRB pulse may occur in the outer regions of the magnetosphere for longer rotation periods, $P\geq 1$ second. These losses are suppressed by several effects: (i) the ponderomotive pre-acceleration of background plasma along the direction of wave propagation (losses reduced approximately as $\gamma_\parallel^{3}$: smaller frequency, $ \propto \gamma_\parallel^2$ in power, and times scales stretched, $ \propto \gamma_\parallel$); this acceleration is non-dissipative and is reversed on the declining part of the pulse; (ii) Landau-Pomeranchuk-Migdal effects (long radiation formation length and ensuing destructive interference of scattered waves). In some cases an FRB pulse may be dissipated on external perturbations (e.g., an incoming pulse of Alfven waves): this may produce a pulse of UV/soft X-rays, a swan song of an FRB, possibly detectable by Chandra.