Spectral Structures and Their Generation Mechanisms for Solar Radio Type-I Bursts

Abstract

The fine spectral structures of solar radio type-I bursts were observed by the solar radio telescope AMATERAS. The spectral characteristics, such as the peak flux, duration, and bandwidth, of the individual burst elements were satisfactorily detected by the highly resolved spectral data of AMATEAS with the burst detection algorithm that is improved in this study. The peak flux of the type-I bursts followed a power-law distribution with a spectral index of 2.9-3.3, whereas their duration and bandwidth were distributed more exponentially. There were almost no correlations between the peak flux, duration, and bandwidth. That means there were no similarity shapes in the burst spectral structures. We defined the growth rate of a burst as the ratio between its peak flux and duration. There was a strong correlation between the growth rate and peak flux. These results suggest that the free energy of type-I bursts that is originally generated by non-thermal electrons is modulated in the subsequent stages of the generation of non-thermal electrons, such as plasma wave generation, radio wave emissions, and propagation. The variation of the time scale of the growth rate is significantly larger than that of the coronal environments. These results can be explained by the situation that the source region may have the inhomogeneity of an ambient plasma environment, such as the boundary of open and closed field lines, and the superposition of entire emitted bursts was observed by the spectrometer.

Energetics of small electron acceleration episodes in the solar corona from radio noise storm observations

“…Strictly speaking, if these small scale heating events are the primary contributor to steady-state coronal heating, it is necessary that α < −2 in order to avoid a situation where the total energy diverges (Hudson 1991). Our findings may be contrasted with the range −3.5 < α < −2.8 found by Mercier & Trottet (1997), Ramesh et al (2012) and Iwai et al (2013Iwai et al ( , 2014. Suresh et al (2017) found that α = −2.23 for very small energy releases observed with the Murchison Widefield Array.…”

A Weak Coronal Heating Event Associated with Periodic Particle Acceleration Episodes

“…(e.g. Mercier & Trottet 1997;Iwai et al 2014;Mugundhan et al 2016;Suresh et al 2017). A similar situation is likely to prevail here.…”

Wavelet-based Characterization of Small-scale Solar Emission Features at Low Radio Frequencies

“…The upper end of this flux range approaches the lower end of the flux range for the power-law fits by Mercier & Trottet (1997) (α ≈ −2.9 to −3.6). Iwai et al (2014), in their observational studies of type-I bursts, also report a power-law index of −2.9 to −3.3. The value of α obtained here is also much lower than the power-law index of −3.5 predicted for the low-energy part of the statistical flare spectrum by Vlahos et al (1995).…”