Spectroscopolarimetric sensing of energy deposition into the chromosphere during solar flares .1. Observations

Measurements of linear polarization in hydrogen H alpha and H beta lines, made with the Large Solar Vacuum Telescope of Baikal Astrophysical Observatory and Automated Solar Telescope of Sayan Solar Observatory, affiliated with the Russian Institute of Solar and Terrestrial Physics, are reported in this paper. Short-term polarization associated with solar flares is found to be present in active regions. There is a significant tendency for the H alpha polarization vector to be radial, i.e., in the flare-to-disk-center direction. This polarization may be due to atmospheric bombardment by hecta keV protons. On the other hand, the polarization vector is found to be perpendicular to the radial direction at some locations where the line profile has a typical mustache shape suggesting a bombardment by energetic electrons. The H beta line is also linearly polarized. However, no preferential direction of polarization is found in this line, which is formed more deeply in the solar atmosphere.