An unusual burst at decameter wavelengths. 2. Interpretation

Abstract

The model which describes appearance and process of radio emission of an unusual burst observed by the UTR-2 (Kharkiv, Ukraine) and URAN-2 (Poltava, Ukraine) radio telescopes at 16−28 MHz is proposed. We suppose that the unusual burst is caused by the small ejection initiated by the active region NOAA1222. This behind-limb region was situated at the heights 2.3R_⊙ to 2.8R_⊙, when radio emission of the unusual burst at the second harmonic was started. We believe that due to interaction of this ejection with coronal plasma some electrons were accelerated. These electrons propagating towards and outwards the Sun were sources of the UTR-2, URAN-2 and STEREO-A recorded unusual burst. The mechanism of radio emission was plasma one. The proposed model allows explaining such properties of the unusual burst as its positive and negative drift rates, duration, abrupt stopping of radio emission at 27.5 MHz and its fine frequency structure.