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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.72] Decimetric Type III Radio Bursts with High Starting Frequencies and the Associated Solar Flare Hard X-Ray Emission

F. C. R. Fernandes, H. S. Sawant (INPE, SP, Brazil), J. L. Melendez-Moreno (USP, SP, Brazil), A. O. Benz (Institute of Astronomy, ETH, Zurich, Switzerland), M. Yoshimori (Rikkoyo Univ., Tokyo, Japan), S. R. Kane, J. M. McTiernan (U. California, Berkeley)

We have examined the characteristics of 160 isolated type III decimetric (100-3000 MHz) radio bursts which occurred during the period September 1992 - October 1993. Bursts associated with 13 hard X-ray flares were examined in detail. The radio observations were made with the PHOENIX solar radio spectrometer in Zurich. The X-ray flares were observed by the Hard X-ray Spectrometer (HXS) on the Yohkoh satellite. Type III radio bursts with normal, reverse as well as bi-directional drifts were observed. Characteristic parameters such as starting frequency, bandwidth, total duration, and frequency drift rate were determined for the radio bursts. Similarly power law photon spectra were fitted to the hard X-ray emission. For an assumed model of ambient density vs. height above the photosphere, the electron beam velocity and hence the electron energy was inferred from the frequency drift rate of the radio burst. Assuming that the energy loss of the energetic electrons is caused primarily by collisions, the height of injection for the radio emitting electrons was deduced. For comparison, characteristics of the energetic electrons were also inferred from the thick target model for the hard X-ray source. Implications of the results with respect to the acceleration and propagation of energetic electrons in solar flares will be discussed.

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