Modulation of the solar microwave emission by sausage oscillations

TL;DR

This paper investigates how sausage oscillations in solar flaring loops modulate microwave emissions, revealing a highly non-linear response that depends on source width and viewing angle, offering a diagnostic tool for plasma region scales.

Contribution

It introduces a model of microwave modulation by sausage waves considering a plasma slab with Epstein density profile, highlighting non-linear effects and diagnostic potential.

Findings

Microwave response to sausage waves is highly non-linear.

Non-linearity depends on source width and viewing angle.

Potential diagnostic tool for plasma region scales.

Abstract

The modulation of the microwave emission intensity from a flaring loop by a standing linear sausage fast magnetoacoustic wave is considered in terms of a straight plasma slab with the perpendicular Epstein profile of the plasma density, penetrated by a magnetic field. The emission is of the gyrosynchrotron (GS) nature, and is caused by mildly relativistic electrons which occupy a layer in the oscillating slab, i.e., the emitting and oscillating volumes do not coincide. It is shown that the microwave response to the linear sausage wave is highly non-linear. The degree of the non-linearity, defined as a ratio of the Fourier power of the second harmonic to the Fourier power of the principal harmonic, is found to depend on the combination of the width of the GS source and the viewing angle, and is different in the optically thick and optically thin parts of the microwave spectrum. This effect could be considered as a potential tool for diagnostics of the transverse scales of the regions filled in by the accelerated electrons.