Analysis of solar narrow band dm-spikes observed at 1420 and 2695 MHz

¹ Astronomical Institute of the Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic
² Institute for Geophysics, Astrophysics and Meteorology, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
³ INAF - Trieste Astronomical Observatory, Via G.B. Tiepolo 11, 34131 Trieste, Italy

Corresponding author: H. Mészárosová, hana@asu.cas.cz

Received: 20 January 2003
Accepted: 2 June 2003

Abstract

Using both linear and nonlinear methods, narrow band dm-spikes recorded at 1420 and 2695 MHz on June 6, 2000, July 8, 2000, July 12, 2000, July 20, 2000, and March 28, 2001 were analyzed. In particular their time profiles were studied statistically. The mean characteristic times of the ascending and of the decaying parts of their profiles are comparable, even if the dispersion of the values is very broad. For selected spikes at 1420 MHz a more precise fitting technique using exponential profiles was applied. While in the decaying part the exponential trend can be generally found, in the ascending part the exponential form can be confirmed only in few cases. The ascending and decaying phase of spikes presumably correspond to the source instability evolution and the plasma wave absorption. Furthermore, durations and polarization values of both 1420 and 2695 MHz spikes were determined and compared with the results in literature. All the analyzed spike events were located near the solar disk center. The polarization values and their trend in spike groups and the nearly constant duration suggest that the polarization originates at the source itself or near it. Selected time series of spikes were tested with respect to low-dimensional determinism and nonlinearity. We found that spikes recorded at fixed frequencies are not governed by a linear stochastic process, as the underlying physical system contains nonlinear signatures.