Synchrotron masers and fast radio bursts

TL;DR

This paper explores how synchrotron masers, generated under specific electron conditions, could explain the coherent emission and rapid variability observed in Fast Radio Bursts, offering an alternative to particle bunching models.

Contribution

It introduces the concept of synchrotron masers with narrow electron pitch angle distributions as a viable mechanism for FRBs, relaxing previous size and density constraints.

Findings

Synchrotron masers can produce the high brightness temperatures of FRBs.

Narrow electron pitch angle distributions are key to maser formation.

This mechanism relaxes the size constraints on FRB sources.

Abstract

Fast Radio Bursts (FRBs), with a typical duration of 1 ms and 1 Jy flux density at GHz frequencies, have brightness temperatures exceeding 1e33 K, requiring a coherent emission process. This can be achieved by bunching particles in volumes smaller than the typical wavelength, but this may be challenging. Alternatively, we can have maser emission. Under certain conditions, the synchrotron stimulated emission process can be more important than true absorption, and a synchrotron maser can be created. This occurs when the emitting electrons have a very narrow distribution of pitch angles and energies. This process overcomes the difficulties of having extremely dense bunches of particles and relaxes the light crossing time limits, since there is no simple relation between the actual size of the source and the observed variability timescale.