Scintillation can explain the spectral structure of the bright radio burst from SGR 1935+2154

TL;DR

This paper investigates whether interstellar scintillation can explain the spectral structure of a bright radio burst from magnetar SGR 1935+2154, providing insights into the burst's emission region and challenging close-in emission models.

Contribution

It models scintillation effects to explain spectral variations in the FRB, constraining the emission region location relative to the magnetar.

Findings

Scintillation can account for the spectral structure with a superluminal apparent velocity >9.5c.

Two spectral components could originate from separate regions spaced >8.3×10^4 km.

The results favor far-away emission models over close-in magnetospheric models.

Abstract

The discovery of a fast radio burst (FRB) associated with a magnetar in the Milky Way by the Canadian Hydrogen Intensity Mapping Experiment FRB collaboration (CHIME/FRB) and the Survey for Transient Astronomical Radio Emission 2 (STARE2) has provided an unprecedented opportunity to refine FRB emission models. The burst discovered by CHIME/FRB shows two components with different spectra. We explore interstellar scintillation as the origin for this variation in spectral structure. Modeling a weak scattering screen in the supernova remnant associated with the magnetar, we find that a superluminal apparent transverse velocity of the emission region of $>9.5\,c$ is needed to explain the spectral variation. Alternatively, the two components could have originated from independent emission regions spaced by $>8.3\times10^4\,$km. These scenarios may arise in "far-away" models where the emission originates from well beyond the magnetosphere of the magnetar (for example through a synchrotron-maser mechanism set up by an ultra-relativistic radiative shock), but not in "close-in" models of emission from within the magnetosphere. If further radio observations of the magnetar confirm scintillation as the source for the observed variation in spectral structure, this scattering model thus constrains the location of the emission region.