A Unified Model of Cosmic Ray Propagation and Radio Extreme Scattering Events from Intermittent Interstellar Structures

TL;DR

This paper presents a unified model linking magnetic interstellar structures to both cosmic ray diffusion and radio scattering events, explaining observations without free parameters and suggesting observational tests with upcoming radio instruments.

Contribution

It introduces a model where magnetic/density sheets account for both cosmic ray propagation and extreme scattering events, with specific geometric constraints and testable predictions.

Findings

Magnetic sheets can explain cosmic ray mean free paths.

The same structures account for radio wave scattering phenomena.

Model predictions can be tested with future radio observations.

Abstract

Intermittent magnetic structures are a plausible candidate for explaining cosmic-ray (CR) diffusion rates derived from observed CR energy spectra. Independently, studies of extreme scattering events (ESEs) of radio quasars and pulsar scintillation have hinted that very straight, large-aspect-ratio, magnetic current sheets may be responsible for the localized large scattering of radio waves. The required shortest axis of the typical structures producing ESEs is of the same scale ($\sim$AU) as the gyroradii of $\sim$GeV CRs. In this paper, we propose that the same magnetic/density sheets can produce large scattering of both CRs and radio waves. We demonstrate that the geometry and volume filling factor of the sheets derived from quasar ESEs can explain the observed mean free path of GeV CRs without introducing free parameters. The model places constraints on the sheet geometry, such as straightness and large aspect ratio, and assumes the statistics of the sheets are similar throughout the Galactic volume. We, therefore, discuss observational tests of the sheet model, which includes observations of echoes in pulsars and fast radio bursts, gravitationally lensed quasars, the distribution of ESE durations, and spatial correlations between ESE events and rotation-measure fluctuations. Such tests will be enabled by upcoming wide-field radio instruments, including Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) and Deep Synoptic Array 2000 Antennas (DSA-2000).