Unusual Solar Radio Burst Observed at Decameter Wavelengths

TL;DR

This paper reports the observation of an unusual solar radio burst at decameter wavelengths with unique properties, including atypical frequency drift and fine structure, and proposes a model to explain it.

Contribution

It presents the first detailed analysis of an unusual solar radio burst with distinctive features and introduces a new interpretative model.

Findings

The burst had a positive frequency drift above 22 MHz and negative below.

Maximum flux reached approximately 1000 s.f.u.

The burst exhibited a fine structure of stripes with 300-400 kHz bandwidth.

Abstract

An unusual solar burst was observed simultaneously by two decameter radio telescopes UTR-2 (Kharkov, Ukraine) and URAN-2 (Poltava, Ukraine) on 3 June 2011 in the frequency range 16-28 MHz. The observed radio burst has some unusual properties, which are not typical for the other types of solar radio bursts. The frequency drift rate of it was positive (about 500 kHz s$^{-1}$) at frequencies higher than 22 MHz and negative (100 kHz s$^{-1}$) at lower frequencies. The full duration of this event varies from 50 s up to 80 s, depending on the frequency. The maximum radio flux of the unusual burst reaches $\approx 10^3$ s.f.u and its polarization does not exceed 10%. This burst has a fine frequency-time structure of unusual appearance. It consists of stripes with the frequency bandwidth 300-400 kHz. We consider that several accompanied radio and optical events observed by SOHO and STEREO spacecraft are possibly associated with the reported radio burst. A model that may interpret the observed unusual solar radio burst is proposed.