Magnetic Field, Electron Density and Their Spatial Scales in Zebra Pattern Radio Sources

Abstract

Zebra patterns (zebras) play an important role in the plasma diagnostics during solar flares. Considering their double plasma resonance (DPR) model, we present an improved method for the determination of the gyro-harmonic numbers of the zebra stripes that are essential in determining the electron density and magnetic field strength in zebra sources. Furthermore, we present the magnetic field and density spatial scales in zebra sources. Compared to the previous method, we change the basic assumption of the method. Namely, the assumption that the ratio $R={L_{\mathrm{bh}}} / {L_{\mathrm{nh}}}$ ( $L_{\mathrm{bh}}$ and $L_{\mathrm{nh}}$ are the magnetic field and density scales) is constant in the whole zebra source is changed to its more generalized form, where the ratio $R$ is a linear function. Using this improved method, first, we determine the gyro-harmonic numbers of several observed zebras and variations of the spatial scales. Then, knowing the gyro-harmonic numbers of zebra stripes, we compute the electron plasma density and magnetic field strength in zebra sources. It is shown that in all cases the gyro-harmonic numbers of zebra stripes are quite high (> ≈50). This significantly reduces the magnetic field strength and thus increases the plasma beta parameter in zebra sources. The change in the ratio of the magnetic field and density scales along the axis of the radiating tube for the studied zebras is within ± 5 percent. For zebras at high frequencies, this ratio increases with the height, and for zebras at lower frequencies it decreases. The ratio of the magnetic field and density scales across the radiating tube is close to 1 and varies in the range 0.87–1.20.