Radio Astronomical Tools for the Study of Solar Energetic Particles I. Correlations and Diagnostics of Impulsive Acceleration and Particle Propagation

Abstract

Solar energetic particles (SEPs) are sporadically ejected from the Sun during flares and coronal mass ejections. They are of major astrophysical interest, because the proximity of the Sun allows for detailed multi-messenger studies. They affect space weather due to interactions with electronics, with the Earth’s atmosphere, and with humans if they leave the protective shield of the magnetosphere of the Earth. Since early studies in the 1950s, starting with particle detectors on the ground, SEP events have been related to radio bursts. Two subjects are addressed in this chapter: attempts to establish quantitative correlations between SEPs and microwave bursts produced by gyro synchrotron radiation of mildly relativistic electrons, and the information derived from type III radio bursts on impulsive processes of particle acceleration and the coronal and interplanetary propagation. Type III radio bursts produced by electron beams on open magnetic field lines have a wide range of applications, including the identification of acceleration regions, the identification of confined particle acceleration with coronal signatures, but no SEPs, and the paths that the electrons, and energetic charged particles in general, take to travel from the low corona to the Heliosphere in case they escape. Simple scenarios of coronal particle acceleration are confirmed in relatively simple and short events. But the comparison with particle transport models shows that longer and delayed acceleration episodes exist especially in large SEP events. They will be discussed in a companion chapter.

Metric type-II radio bursts and space weather phenomena: A statistical study

“…The dominant emission mechanism from the metric (m) to decametric−hectometric (DH) wavelengths is the plasma emission, which links the observed radio frequency to the electron density of the medium. Together with its wide observation domain, the radio emissions in the m−DH wavelength range carry out a rich diagnostic potential for solar physics and space weather (SW) research (Klein, 2021a). The term SW refers to the influence of solar activity in the heliosphere, the planetary magnetospheres, atmospheres and surface, the effects to space-borne and ground-based technology as well as the risks to the astronaut's health and life (Pulkkinen, 2007;Temmer, 2021).…”

Release Episodes of Electrons and Protons in Solar Energetic Particle Events

“…Type III radio bursts emerge from electrons that are accelerated in processes associated with solar flares, wherein they propagate along open magnetic field lines outward from the Sun [12]. Those are associated with "impulsive" SEPs, but, more importantly, type III bursts provide direct observational evidence of the opening of the magnetic field lines, which is a prerequisite for the escape of particles into field lines that magnetically connect them to the observer [13]. Moreover, type II radio bursts are associated with electron beams accelerated at shock waves and usually with "gradual" SEP events [14] when a significant solar event takes place.…”

DLITE—An inexpensive, deployable interferometer for solar radio burst observations

“…McCauley et al (2017) used the Murchison Widefield Array (MWA; Li et al, 2018) to perform spectroscopic imaging of a series of Type III bursts, tracking them over several frequencies to illustrate their evolution from a single source in the inner corona to two separate sources split between two separate flux tubes. Type III bursts can also provide insights into SEP events (Klein, 2021) because of their association with escaping electron beams.…”