Solar S-bursts observed by the radio telescope UTR-2 in the period 2001 -2002 are studied. The bursts chosen for a detailed analysis occurred in the periods 23 -26 May 2001, 13 -16 and 27 -39 July 2002 during three solar radio storms. More than 800 S-bursts were registered in these days. Properties of S-bursts are studied in the frequency band 10 -30 MHz. All bursts were always observed against a background of other solar radio activity such as type III and IIIb bursts, type III-like bursts, drift pairs and spikes. Moreover, Sbursts were observed during days when the active region was situated near the central meridian. Characteristic durations of S-bursts were about 0.35 and 0.4 -0.6 s for the May and July storms, respectively. For the first time, we found that the instantaneous frequency width of S-bursts increased with frequency linearly. The dependence of drift rates on frequency followed the McConnell dependence derived for higher frequencies. We propose a model of S-bursts based on the assumption that these bursts are generated due to the confluence of Langmuir waves with fast magnetosonic waves, whose phase and group velocities are equal.

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The properties of powerful (flux > 10 −19 W m −2 Hz −1 ) type III bursts observed in July -August 2002 by the radio telescope UTR-2 at frequencies 10 -30 MHz are analyzed. Most bursts have been registered when the active regions associated to these bursts were located near the central meridian or at 40°-60°to the East or West from it. All powerful type III bursts drift from high to low frequencies with frequency drift rates 1 -2.5 MHz s −1 . It is important to emphasize that according to our observations the drift rate is linearly increasing with frequency. The duration of the bursts changes mainly from 6 s at frequency 30 MHz up to 12 s at 10 MHz. The instantaneous frequency bandwidth does not depend on the day of observations, i.e. on the disk location of the source active region, and is increasing with frequency.The results of observational properties are discussed in the frame of the standard plasma model of type III bursts radio emission.

International audienceThe current status of the large decameter radio telescope UTR-2 (Ukrainian T-shaped Radio telescope) together with its VLBI system called URAN is described in detail. By modernization of these instruments through implementation of novel versatile analog and digital devices as well as new observation techniques, the observational capabilities of UTR-2 have been substantially enhanced. The total effective area of UTR-2 and URAN arrays reaches 200 000 m2, with 24 MHz observational bandwidth (within the 8–32 MHz frequency range), spectral and temporal resolutions down to 4 kHz and 0.5 msec in dynamic spectrum mode or virtually unlimited in waveform mode. Depending on the spectral and temporal resolutions and confusion effects, the sensitivity of UTR-2 varies from a few Jy to a few mJy, and the angular resolution ranges from ~ 30 arcminutes (with a single antenna array) to a few arcseconds (in VLBI mode). In the framework of national and international research projects conducted in recent years, many new results on Solar system objects, the Galaxy and Metagalaxy have been obtained. In order to extend the observation frequency range to 8–80 MHz and enlarge the dimensions of the UTR-2 array, a new instrument – GURT (Giant Ukrainian Radio Telescope) – is now under construction. The radio telescope systems described herein can be used in synergy with other existing low-frequency arrays such as LOFAR, LWA, NenuFAR, as well as provide ground-based support for space-based instruments