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Statistical analysis of solar radio fiber bursts and relations with flares
2021-10-08| 【A A A【Print】【Close】

The dynamic spectrum of solar radio bursts is commonly characterized by various fine structures (FSs). These spectral FSs mainly depend on the energetic particles, on the magnetic field in the source region, and on the detailed flaring processes. As a unique diagnostic tool for understanding the microphysical processes, solar radio FSs can provide direct information about energetic particles and the radiation source region, such as the magnetic field, the plasma parameters, particle acceleration, and propagation. Radio fiber bursts belong to one of the most particular FSs embedded in the solar-type IV continuum. They usually appear in groups, and their prominent characteristic is the intermediate drifting rate.

A statistical study of fiber bursts may contribute to establishing general rules and setting constraints on its formation mechanisms. However, there is still no report about the relations of the observed parameters of fiber bursts and the flaring processes, especially at frequency above 1 GHz.

This work presents a detailed investigation of fiber bursts in the frequency range of 1.10-2.06 GHz and 2.60-3.80 GHz observed by the Solar Broadband Radio Spectrometers (SBRS/Huairou) of the National Astronomical Observatories of China (NAOC) from 2000 to 2006.

The researchers found that more than 40% of radio fiber events occurred in the preflare and rising phases of the associated solar flares. At the same time, most fiber events are temporally associated with hard X-ray bursts or microwave bursts, which implies that they are closely related to nonthermal energetic electrons. Most fiber bursts are strongly polarized, and their average duration, relative bandwidth, and relative frequency-drift rate are about 1.22 s, 6.31%, and -0.069 s–1. The average duration and relative bandwidth of fiber bursts increase with solar flare class. The fiber bursts associated with X-class flares have a significantly lower mean relative frequency-drift rate. The average durations in the postflare phase are clearly longer than the duration in the preflare and rising phases. The relative drift rate in the rising phase is clearly higher than that in preflare and postflare phases. The hyperbola correlation of the average duration and the relative drift rate of the fiber bursts is very interesting. These characteristics are very important for understanding the formation of solar radio fiber bursts and for revealing the nonthermal processes of the related solar flares. 

Table. Average parameters of 915 individual fibers during different flare phases.

Figure. Statistical histograms of negative-drift individual fiber parameters corresponding to C, M, and X class flares. (a) Duration. (b) Relative bandwidth. (c) Polarization. (d) Relative frequency-drift rate. The dotted red line represents the average of each parameter. Panel c: mean polarization degrees of left- and right-handed circular polarized fibers, respectively.

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