Alternative Models of Zebra Patterns in the Event on June 21, 2011

Abstract

The analysis of the spectral characteristics of the burst radio emission on June 21, 2011 was carried out on the basis of an improved methodology for determining harmonic numbers for the corresponding stripes of the zebra structure. By using the parameters of the zebra structure in the time-frequency spectrum and basing on the double-plasma resonance model, the magnetic field and its dynamics, electron density, and the time variation of the distance between the stripes with harmonics \(s = 55\) and 56 and adjacent stripes near the frequency ≈183 MHz have been determined in the burst generation region. The relationships between the scale characteristics of the field and the density along and across the axis of the power tube and their dependence on time have been also determined. The field obtained (1.5 G for the first harmonic and 0.75 G for the second harmonic of the plasma frequency) turned out to be so small that, firstly, it fails to explain the dynamic features of the spectrum based on MHD waves, and secondly, it results in large values for plasma beta (>1). Other possible difficulties of the generation mechanism of bursts with zebra pattern based on the double-plasma resonance are also noted. Another possible mechanism, with whistlers, explains qualitatively the main observational characteristics of this zebra. The magnetic field required in this case is about 4.5 G, and the plasma beta is 0.14, which fully corresponds to the coronal conditions.