Physics
Scientific paper
Jun 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt..........f&link_type=abstract
PhD Dissertation, INPE-6396-TDI/612
Physics
1
X Ray Sources, Frequency Ranges, Broadband, Electric Fields, Imaging Techniques, Ion Acoustic Waves, Radio Emission, Spectral Resolution, Spectrum Analysis, Solar Radio Bursts, Statistical Analysis, X Rays, Hypotheses, Low Frequencies, Plasmas (Physics)
Scientific paper
Here we present the author's contribution in the development of the two phases of the Wide Band (200-2500 MHz) Digital (100 channels) Decimetric Spectroscope (WDDHRS) with high time (10-1000 ms) and frequency (3-10 MHz) resolutions and with high sensitivity (approximately 2 sfu), unique in the southern hemisphere, which is in regular operation since May 1996, at INPE in Sao Jose dos Campos. The WDDHRS has flexibility to choose the frequency range of the observations and resolutions. Patch-like emission showing a split in frequency was discovered for the first time. An emission mechanism based on the coalescence between Langmuir waves excited by electron beams and ion-acoustic waves is suggested, which accounts for the observed properties of this type of emission. For the first time a statistical analysis of 102 decimetric type III solar bursts observed in the (1600 +/- 50/100) MHz range is presented. Observed properties suggested that the decimetric type III bursts are generated by beam plasma interaction at the second harmonic. In continuation of the analysis of the decimetric III burst, 160 individual type III bursts, the majority of which were observed above 1000 MHz, observed by the PHOENIX Radio Spectrometer, were also analysed in detail. The most important result is that 2/3 of the decimetric type III bursts showed reverse slope drift rate. Considering the average energy associated with the electron beam and assuming the beam loss energy mainly by collision with the ambient plasma, the height of the injection of the electron beam above the photosphere is determined. The YOHKOH satellite offers high spectral resolution and high energy solar X-ray bursts observations. Analysis of the 13 solar flares associated with radio emission also is presented for various aspects such as spectral analysis, ratio of low to high energy photons, imaging at various energies, and association with type III bursts. The time evolution of the spectral analysis showed that the typical trend is soft-hard-soft and in general the spectrum is best fitted by a double power law with a break in energy at approximately 100 keV. Higher energies are delayed in comparison with low energies. Impulsive acceleration/injection due to an electrical field explains most of the observed and estimated source parameters. The investigation of the association between the radio and X-rays showed that in two flares, at the beginning X-rays are better correlated with low frequency. However, during the time evolution of the flare X-rays are better correlated with higher frequencies, suggesting that the acceleration region travels downward towards the photosphere. In three flares it was observed that radio emissions occur before the peak of the X-rays confirming the hypothesis that decimetric emission is occurring near the acceleration
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