Solar bursts gyrosynchrotron emission from three-dimensional sources

¹ Instituto Nacional de Pesquisas Espaciais – INPE, Av. dos Astronautas, 1758 J. da Granja 515, 12227-010 São José dos Campos SP, Brazil e-mail: paulo@craam.mackenzie.br
² Centro de Rádio Astronomia e Astrofísica Mackenzie – CRAAM, Rua da Consolação, 896, Ed. Amantino Vassão, 01302 São Paulo SP, Brazil


Received: 8 December 2005
Accepted: 23 February 2006

Abstract

Aims.In this study we have analyzed the spectral and spatial characteristics of gyrosynchrotron emission and the polarization of solar bursts in a highly inhomogeneous medium. Our main goal was to investigate the effects of the geometry of the source on the resulting spectrum.

Methods.The SOHO/EIT and TRACE high resolution images revealed structured magnetic configurations in detail over solar active regions. In our method, we represent the magnetic field geometry by three-dimensional structures obtained from magnetic field extrapolation, tomography, or any geometry that resembles the observed structures. The gyrosynchrotron radiation was numerically calculated through a modified version of Ramaty's code.

Results.We calculated the radiation produced by non-thermal electron distributions in this complex environment and solved the radiative transfer equation. The results, presented in brightness distribution maps, polarization maps, and spectra, are discussed. Our numerical results agree with statistical analyses of observed spectra present in the literature. We note a spectral broadening due to the spatial and intensity inhomogeneity of the magnetic field and no center-to-limb variations, which cannot be explained by homogeneous source models. The computed maps revealed a non uniform brightness distribution, with small-scale structures, and different spatial characteristics in each frequency. Also, we found different spectral characteristics at different regions of the emitting source. Polarization maps reveal its high dependence on geometry and on the position of the source on the solar disk.