Constraining the nature of FRB-emitting bunches via photo-magnetic cascades

TL;DR

This paper investigates the particle bunch properties responsible for FRBs within the coherent curvature radiation model, showing that photo-magnetic cascades impose constraints on bunch density and magnetic field line curvature, ruling out rapidly rotating magnetars as sources.

Contribution

It introduces constraints on FRB-emitting particle bunches based on photo-magnetic cascade effects, refining the viable source models within the curvature radiation framework.

Findings

Bunch density must be around 10^{13-14} cm^{-3} to avoid cascades.

Large curvature radii ( > 10^8 cm) are required for bunch propagation.

Rapidly rotating magnetars are unlikely FRB sources in this model.

Abstract

We provide constraints on the nature of particle bunches that power fast radio bursts (FRBs) in the coherent curvature radiation model. It has been shown that current-induced perturbation to the motion of individual particles results in a high-energy, incoherent component of emission. We consider photo-magnetic interactions and show that the high-energy radiation can produce pairs which screen the accelerating electric field. We find that to avoid catastrophic cascades that quench emission, bunches capable of producing FRBs must have a modest density $n_e \approx 10^{13-14}\, {\rm cm^{-3}}$, and likely propagate along field lines with large curvature radii, $\rho > 10^8 \, {\rm cm}$. This rules out rapidly rotating magnetars as FRB sources within the coherent curvature radiation model.