Fast Radio Burst Breakouts from Magnetar Burst Fireballs

TL;DR

This paper proposes that magnetar X-ray bursts create an electron-positron outflow that can suppress or allow the escape of associated fast radio bursts, providing insights into their emission mechanisms and observational signatures.

Contribution

It introduces a model where high-temperature X-ray bursts produce an electron-positron outflow that influences FRB breakout, linking magnetar activity to FRB observability.

Findings

FRBs can break out if emitted beyond a few tens of NS radii.

FRB strength and X-ray burst intensity determine if the FRB is choked.

High-temperature X-ray bursts are likely essential for FRB occurrence.

Abstract

The recent discovery of a Mega-Jansky radio burst occurring simultaneously with short X-ray bursts from the Galactic magnetar (strongly magnetized neutron star (NS)) SGR 1935+2154 is a smoking gun for the hypothesis that some cosmological fast radio bursts (FRBs) arise from magnetar bursts. We argue that the X-ray bursts with high temperature $T \gtrsim 30$ keV entail an electron--positron ($e^{\pm}$) outflow from a trapped--expanding fireball, polluting the NS magnetosphere before the FRB emission. The $e^{\pm}$ outflow is opaque to FRB photons, and is strongly Compton-dragged by the X-ray bursts. Nevertheless, the FRB photons can break out of the $e^{\pm}$ outflow with radiation forces if the FRB emission radius is larger than a few tens of NS radii. A FRB is choked if the FRB is weaker or the X-ray bursts are stronger, possibly explaining why there are no FRBs with giant flares and no detectable X-ray bursts with weak FRBs. We also speculate that the $e^{\pm}$ outflow may be inevitable for FRBs, solving the problem of why the FRBs occur only with high-$T$ X-ray bursts. The breakout physics is important for constraining the emission mechanism and electromagnetic counterparts to future FRBs.