Details

Autor(en) / Beteiligte

• da Silva, Adriana Valio Roque

Titel

Multi-wavelength observations of solar flares with emphasis on the millimeter emission

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

1995

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• In this work, we study a total of 10 solar flares observed by the Berkeley-Illinois-Maryland millimeter interferometer (BIMA). All flares were simultaneously observed in soft X-rays, and some of the events were also detected in hard X-rays, H$\alpha$, and at microwave wavelengths. The great majority of flares for which images were available showed multiple sources whose physical characteristics varied considerably from one source to another, and moreover, different sources were seen at distinct wavelengths. We used the microwave/hard X-ray/soft X-ray emissions from individual sources to determine the radio emission mechanisms, the energetic electron population, the magnetic field strength, and plasma density. After BIMA's upgrade to six antennae, the first images of a flare (1994 August 17) at millimeter wavelength during its gradual phase showed the emission to be consistent with the predicted free-free flux from the soft X-ray isothermal looptop source and a multi-temperature footpoint source with a hot and a cold components. Most of the millimeter flux density, however, originates from the top of the magnetic loop. Five flares were observed only at millimeter and non-imaging soft X-ray wavelengths, these also show the millimeter emission during the gradual phase to be consistent with optically thin free-free flux density from the soft X-ray emitting plasma. A high resolution radio spectrum consisting of microwave and millimeter (86 GHz) emissions was constructed in order to determine the radio emission mechanism. These combined radio spectra have shown the impulsive phase of the radio emission to be due to nonthermal gyrosynchrotron from electrons with a power-law differential energy spectrum of slope $\delta\sb{r}\sim$ 3-4. Comparisons of high spectral resolution hard X-ray and microwave observations provide information on the accelerated electrons that produced the emission at both wavelengths. The power-law index of the differential energy spectrum of electrons that produced the hard X-rays is always found to be steeper ($\delta\sb{x}\sim$ 5-8) than the index of the radio producing electrons ($\delta\sb{r}\sim$ 3-4). Since the temporal evolution of both radio and hard X-ray emissions is similar, and the sources at both wavelengths are seen to coincide in location (when images are available), we conclude that the energy distribution has a power-law index $\delta = \delta\sb{x}\sim$ 5-8 for energies below a break energy (100-300 keV) and $\delta = \delta\sb{r}\sim$ 3-4 above this break energy.