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    Tese
    Análise de explosões solares em 45 e 90 ghz observadas por POEMAS com medidas de polarização
    Silva, Douglas Félix da (2020-03-26)

    Escola de Engenharia Mackenzie (EE)

    Solar flares, resulting from the activity of the Sun, are among the most energetic phenomena in the Solar System, and in the most extreme cases directly affect our highly technological society. In this work, we analyze solar flares detected at millimeter, centimeter, and X-ray wavelengths. Solar flares observed in these energy bands allow the diagnostics of accelerated electrons and magnetic field values where the radio emission is produced. To better understand the accelerated electrons and magnetic fields involved in the flares, two methods were explored. We report on the first use of polarization masurements of solar flares at millimetre wavelengths to investigate the configuration of the magnetic field and determine the population of accelerated electrons by studying the signatures of radio and hard X-ray spectra. To model the magnetic configuration, two solar flares were analyzed. These were observed by the POlarization Emission of the Millimeter Activity of the Sun system (POEMAS) telescopes. Additional spectral data at microwaves from 1 to 15 GHz were obtained from the Radio Solar Telescope Network (RSTN) and at high frequencies (212 and 405 GHz) by the Submillimetre Solar Telescope (SST). X-ray data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) were used to characterize the morphology of the source, also the 335 Å images and magnetograms of active regions from the Solar Dynamic Observatory (SDO) were used to infer the magnetic loop geometry. The flux density and polarization spectra at radio wavelengths were fit using a model simulating the gyroemission in a 3D structure of a non-homogeneous magnetic loop. The second approach analyses the accelerated particles at different frequencies. For this, we investigated ten solar flares that occurred between 2011 and 2013, observed in radio from 5 to 212 GHz (RSTN, POEMAS, SST) and X-rays up to 300 keV and 1000 keV in one case (Rhessi and Fermi). The spectral index was calculated by fitting the Ramaty gyrosynchrotron emission model to the observed radio spectrum, while the hard X-ray spectra were fitted using a model of thermal plus nonthermal emission of accelerated electrons with a power-law distribution. Finally, the results of both indices were compared, yielding a harder radio index than that obtained in X-rays. Except for one event detected by Fermi up to 1 MeV that was studied in detail