EDP Sciences
Free access
Volume 366, Number 1, January IV 2001
Page(s) 326 - 330
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20000221

A&A 366, 326-330 (2001)
DOI: 10.1051/0004-6361:20000221

High-sensitivity observations of solar flare decimeter radiation

A. O. Benz, P. Messmer and C. Monstein

Institute of Astronomy, ETH-Zentrum, 8092 Zurich, Switzerland

(Received 25 May 2000 / Accepted 7 November 2000 )

A new acousto-optic radio spectrometer has observed the 1-2 GHz radio emission of solar flares with unprecedented sensitivity. The number of detected decimeter type III bursts is greatly enhanced compared to observations by conventional spectrometers observing only one frequency at the time. The observations indicate a large number of electron beams propagating in dense plasmas. For the first time, we report weak, reversed drifting type III bursts at frequencies above simultaneous narrowband decimeter spikes. The type III bursts are reliable signatures of electron beams propagating downward in the corona, apparently away from the source of the spikes. The observations contradict the most popular spike model that places the spike sources at the footpoints of loops. Conspicuous also was an apparent bidirectional type U burst forming a fish-like pattern. It occurs simultaneously with an intense U-burst at 600-370 MHz observed in Tremsdorf. We suggest that it intermodulated with strong terrestrial interference (cellular phones) causing a spurious symmetric pattern in the spectrogram at 1.4 GHz. Symmetric features in the 1-2 GHz range, some already reported in the literature, therefore must be considered with utmost caution.

Key words: acceleration of particles -- Sun: corona -- Sun: flares -- Sun: magnetic fields -- Sun: radio radiation

Offprint request: A. O. Benz, benz@astro.phys.ethz.ch

© ESO 2001