Astronomy and Astrophysics – Astrophysics
Scientific paper
1999-12-23
Astronomy and Astrophysics
Astrophysics
Astronomy and Astrophysics, in press
Scientific paper
The minimum and the mean bandwidth of individual narrowband spikes in two events in decimetric radio waves is determined by means of multi-resolution analysis. Spikes of a few tens of millisecond duration occur at decimetric/microwave wavelength in the particle acceleration phase of solar flares. A first method determines the dominant spike bandwidth scale based on their scalegram, the mean squared wavelet coefficient at each frequency scale. This allows to measure the scale bandwidth independently of heuristic spike selection criteria, e.g. manual selection. The major drawback is a low resolution in the bandwidth. To overcome this uncertainty, a feature detection algorithm and a criterion for spike shape in the time-frequency plane is applied to locate the spikes. In that case, the bandwidth is measured by fitting an assumed spike profile into the denoised data. The smallest FWHM bandwidth of spikes was found at 0.17 % and 0.41 % of the center frequency in the two events. Knowing the shortest relevant bandwidth of spikes, the slope of the Fourier power spectrum of this two events was determined and no resemblance to a Kolmogorov spectrum detected. Additionally the correlation between spike peak flux and bandwidth was examined.
Benz Arnold O.
Messmer Peter
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