Alternative zebra-structure models in solar radio emission

TL;DR

This paper explores alternative models for the zebra structure in solar radio emissions, proposing mechanisms involving explosive instability and proton scattering, challenging traditional explanations like double plasma resonance.

Contribution

It introduces new mechanisms involving explosive instability and proton scattering to explain zebra structures, expanding beyond existing models like double plasma resonance.

Findings

Explosive instability can generate zebra structures in solar radio emissions.

Proton scattering on ionic sound harmonics produces electromagnetic waves resembling ZS stripes.

The proposed mechanisms may also explain zebra-like features in pulsar radio emissions.

Abstract

In the literature, discussion continues about the nature of the zebra structure (ZS) in type IV radio bursts, and understanding even the most extended mechanism associated with double plasma resonance has been improved in series of works. Moreover, in the recent work (Ben\'a\v{c}hek, Karlick\'y, Yasnov, 2017) its ineffectiveness was shown under the usually adopted conditions in the radio source. In this case in a number of works we demonstrated the possibility of modeling with whistlers to explain many thin components of ZS stripes, taking into account the effects of scattering whistlers on fast particles. This situation stimulates the search for new mechanisms. For example, earlier we showed the importance of explosive instability, at least for large flares with the ejections of protons. In the system a weakly relativistic beam of protons, nonisothermic plasma, the slow beam mode of the space charge possesses negative energy, and in the triplet slow and fast beam modes and ion acoustic wave an explosive cascade of harmonics from ionic sound is excited. Electromagnetic waves in the form of ZS stripes appear as a result of the fast protons scattering on these harmonics. Such a mechanism can also be promising for a ZS in radio emission from the pulsar in the Crab nebula.