This study offers an explanation of the impact linear polarization observed during an impulsive phase of the 2??/4.8?? flare on July 23, 2002, with the Large Solar Vacuum Telescope (LSVT). A high degree of polarization and a deep central reversal of the ???? line were detected only in a small region of the flare's southern ribbon. An accurate comparison of LSVT high-resolution spectro-polarimetric data with the hard X-rays observed by the Reuven Ramaty High Energy Solar Spectroscopic (RHESSI) revealed that these effects on the ???? line profile were seen in the region (~10") which was located between two hard X-ray footpoints over the southern ribbon. At the same region, according to RHESSI data were locations of the gamma-ray sources (in the 0.3?C0.5 and 0.7?C1.4 MeV bands) which are caused by electron bremsstrahlung. We assume that two hard X-ray footpoints make a common footpoint of the southern branch of the loop, which is divided into two due to the high-energy electron flux. Injection of the high-energy and relativistic electron flux into the dense chromospheric layers might have caused the impact polarization and central reversal of the ???? line in the southern ribbon contrary to the northern one with no polarization and with a typical footpoint of ~20-120 keV hard X-rays.
Authors: N.M. Firstova
Publication Status: Astronomy Letters
Last Modified: 2015-02-03 10:58
Hα line impact linear polarization observed in the 23 July 2002 flare with the Large Solar Vacuum Telescope (LSVT)
We represent results of research of proton flare 2B/X4.8, observed on the Large Solar Vacuum Telescope (LSVT) at the Baikal Astrophysical Observatory in a spectropolarimetric mode with high spatial and spectral resolution. We have found evidence for Hα line impact linear polarization in several cases, predominantly, during the initial moments of flare. Of the ? α line 606 cuts made along dispersion in 53 spectrograms, a polarizing signal was found more or less confidently found in 60 cuts (13 spectrograms). Mainly, polarization was observed in one kernel of flare. A typical feature of this kernel was that line was observed with a reversal in the central part of this kernel that created a dip in the kernel center in a photometric cut. The size of these dips and the size of sites with the linear polarization coincide and are equal 3-6 arc sec. The maximum polarization degree in this kernel reached 15 %. The polarization direction in the kernel is radial except for first two frames with the polarization direction was both radial and tangential. Thus, there is an analogy of the effects observed at the chromospheric level in this kernel (polarization and depression in line cernel) with the temporal variation of the HXR sources.