(1) Institute of Radio Astronomy, Kharkov, Ukraine(2) Space Research Institute, Graz, Austria

Decameter Type IV bursts: Properties of Fiber Bursts

V.N. Melnik (1), A.A. Konovalenko (1), H.O. Rucker (2), E.P. Abranin (1), V.V. Dorovskyy (1), F.F.Stanislavskyy (1)

UTR-2 radio telescope

Effective area 150000 sq.mWorking frequencies 10-30MHz

Sensitivity 5 Jy Beam at 25 MHz 30’

Type IV bursts observed on July, 13, 2004 and on July, 23, 30, 31 in 2005.

Duration of Type IV bursts is a little more than 1 hour

185, 186 , 251, 236 fiber bursts were analyzed.

July, 23, 2005

Its duration is about 1 hour

Type IV burst consists from two parts

July, 30, 2005

Decreasing part of intensive Type IV burst, which lasted more than 6 hours.

July, 31, 2005

Duration of Type IV burst >7 hours

July, 31, 2005July, 23, 2005

Histograms of fiber bursts on frequency width

Frequency band from 3 to 12MHz with average value 6-7 MHz

July, 13, 2004 July, 31, 2005

Distributions of fiber bursts on drift rates

The main part of the bursts has drift rates from 1 MHz/s to 4 MHz/s

For events of July, 13, 2004 and July, 23, 2005 the larger part of bursts have negative drift rates and for events of July, 30 and 31, 2005 there is the approximate equal number of bursts with negative and positive drift rates

July, 23, 2005 July, 30, 2005.

Duration histograms of fiber bursts

Durations of fiber bursts change mainly in the range from 3 to 12 s. These values are again close to those for usual Type III bursts

July, 23, 2005 July, 31, 2005

Radio emission fluxes for fiber bursts of Type IV bursts

Fluxes of radio emission change dramatically from some s.f.u. for 23 July event up to 100 s.f.u. for 13 July and 30 July events and even 10000 s.f.u. for 31 July event.

All observed decameter Type IV bursts have fine structure in the form of sub-bursts (fiber bursts) both in emission and absorption. Such important characteristics as duration and frequency drift rates are close to those for usual Type III bursts observed in frequency range 10-30MHz. It says apparently that fiber bursts are generated by electron beams with linear velocities and densities, which are close to those for Type III electrons. In favor of it says the change in wide range of radio fluxes of fiber bursts, which are also analogous to that for Type III bursts. The fact that in all Type IV bursts there are fiber bursts with negative and positive drift rates means that electron beams propagate towards and outwards to the Sun. At the same time the limited frequency band of appearance of fiber bursts points out preferred heights, at which these bursts generated.

Conclusions