Intensity and polarization of the hard X-ray radiation of solar flares at the top and footpoints of a magnetic loop

The spatial distributions of the intensity and polarization of hard X-rays (HXR) were modeled based on a numerical solution of the nonstationary kinetic Fokker-Plank equation. Two cases of nonstationary long injections (∼10 s) of nonthermal electrons at the top of a flaring loop are considered. In the first case, the injection occurs anisotropically in a cone directed along the field to one of the loop’s footpoints. In the second case, electrons are injected isotropically. In the case of the anisotropic injection, the degree of HXR polarization in the footpoints is low and does not exceed 8%. At the same time, the polarization of the radiation from the top in a range of photon energies from 30 to 60 keV reaches 43% at the beginning of injection. Significantly different spatial distributions of HXR characteristics are obtained for the isotropic injection of electrons. In this case, the calculated degree of HXR polarization from the top exhibits a strong variability: it reaches 15–18% at the beginning of injection at photon energies of 30–90 keV, decreases to zero after 5 s, and then, changing its sign, increases to 8%. In the footpoint of the loop, HXR is in fact nonpolarized. The features of the spatial distributions obtained in the simulation process can be measured with X-ray telescopes-polarimeters in future experiments and used for diagnosing the pitch angle distribution of accelerated electrons.