Other
Scientific paper
Nov 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........31c&link_type=abstract
PhD Dissertation, Instituto Nacional de Pesaciais Espaciais Sao Jose dos Campos, Brazil
Other
High Resolution, Millimeter Waves, Radiometers, Fragmentation, Solar Flares, X Ray Spectrometers, Temporal Resolution, Spectral Resolution, Solar Radio Bursts, Radiation Sources, Magnetic Fields, Interferometers, Infrared Tracking, Frequency Ranges
Scientific paper
High-sensitivity, high-spectral-resolution solar observations in the millimeter wavelength are scanty. A sensitive radiometer with I GHz resolution, operating in the frequency range of 18 and 23 GHz in conjunction with 13.7 m diameter antenna has been developed by the author initially, in 1987, for the observations of the solar active regions and later on modified for the bursts observations. At present each frequency is sampled for 100 ms. Details of this instrumentation, including the process of calibration, data acquisition, and reduction are described. The author has participated in the international solar observation campaigns. Sixty seven groups of the solar bursts have been observed by this instrument, 9 observed simultaneously with hard X-ray burst spectrometer on board of Solar Maximum Mission satellite and 5 observed with Frequency Agile Interferometer, operating in the frequency range of (1-18) GHz, of the CALTECH. There is a suggestion that solar flares are composed of small flares named as elementary flare bursts. The counterpart of these bursts in the millimeter wave band is known as "Simple Bursts" of the duration of the order of seconds exhibiting single peak. Occurrence of such burst is rare. Eleven of these bursts have been investigated in detail for their spectral behaviour for the f-irst time. The observed parameters of these bursts are as follows: average rise time approx. 4 s, spectral index varied between - 1.8 and -3.2, and time evolution of the spectral index shows soft-hard-soft behaviour. Short rise time together with observed spectral behaviour suggest the mechanism of the acceleration and injection of the electrons as of impulsive type. High spectral resolution observations in the optically thin part of the spectra permitted to estimate precise spectral index. Observed spectral index and estimated magnetic field suggest that higher energy, approx. 200 keV electrons are involved in the generation of these bursts. Possible mechanism of the acceleration has been also discussed. Source parameters (B = 570 G; E = 100-300 keV; NT = 1033 - 1036 electrons and ET = 1025 - 1027 erg) of the EFB are nearly similar to 'hot points'. We have made first order estimate of millimeter wave emission from such source. Simultaneous investigations of the eight complex millimeter bursts, exhibiting more than one peak, with hard X-rays, have been carried out for the f-irst time with high spectral and temporal resolutions. Here, for the first time we have shown at least in three cases that highest energy of X-rays simultaneously peaking with millimeter wavelength bursts was about 300 keV thus indicating that higher energy electrons up to (200-400) keV are responsible for the generation of the millimeter wavelength bursts. Also estimated are source parameters of the X-ray and microwave sources. In one case we have observed turnover frequency enabling us to estimate more accurate magnetic field and other source parameters.
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