Type IV Bursts at Decameter Wavelengths

V. N. Melnik$^1$, A.A. Konovalenko$^1$, V. Dorovskyy$^1$, H.O. Rucker$^2$, E.P. Abranin$^1$, A.A. Stanislavskyy$^1$, A. Lecacheux$^3$

$^1$Radio Astronomy Institute, Kharkov, Ukraine
$^2$Space Research Institute, Graz, Austria
$^3$Observatoire de Meudon, Paris, France

We report the results of observations of some Type IV bursts, which were registered at radio telescope UTR-2 (Kharkov, Ukraine) during period 2003 - 2005. Detection of Type IV bursts in wide band from 10 to 30 MHz with high sensitivity and time resolution allowed to study their properties. These bursts show increased radio emission with fluxes 10-1000 s.u.f. In some cases such bursts lasted some hours. In all cases Type IV bursts have fine structures in the form of sub-bursts with durations from 2-3 s to 10 s. Their frequency bands were from 1-2MHz to 6-8MHz. For the most of sub-bursts their frequency drift rates were more than 1MHz/s and sign of drift rates was both positive and negative. The Type IV burst observed at July 22, 2004 had zebra structure, in which single zebra stripes had positive, negative and infinite drift rates. For some Type IV bursts we registered bursts in absorption.