A Statistical Survey of Hard X-ray Spectral Characteristics of Solar Flares with Two Footpoints |
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| Authors: | P Saint-Hilaire S Krucker R P Lin |
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| Institution: | (1) Institute of Solar-Terrestrial Physics, Russian Academy of Sciences, Siberian Branch, P.O. Box. 291, Irkutsk 33, 664033, Russia |
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| Abstract: | The impulsive phase of the 23 July 2002 2B/X4.8 proton flare with a classical two-ribbon structure was observed with the Irkutsk
Large Solar Vacuum Telescope (LSVT) in spectropolarimetric mode, with high spatial, spectral, and time resolution. On the
basis of 49 spectrograms and 1200 spectral cuts across the flare ribbons, evidence for Hα line impact polarization has been obtained. A systematic change of the Stokes Q and U parameters has been detected across the ribbons for different flare regions measured with a scanning step of 0.85″. In the
eastern side of the ribbons, the degree of polarization is 4 – 8%; its plane is oriented toward the solar disk center (radial
direction). In the western side, the polarization degree runs up to 25%, and its plane is perpendicular to the disk center
direction (tangential direction). A comparison of these results with hard X-ray data (RHESSI) allows us to conclude that high-energy
electron beams reached the chromosphere during this flare. The observed changes of the direction of polarization and the vanishing
polarization within the ribbons mean that, at the chromospheric level, the energy of electrons remaining in the beam is about
200 eV. A shift of the peak position of polarization relative to the intensity maximum in the ribbons may result from the
inclination of the electron beam axis with respect to the solar surface. |
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| Keywords: | Solar flare Spectrograph Impact polarization |
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