Simulation of a Looptop Hard X-ray Source in Turbulent Plasma of Solar Flares

Abstract

The kinetics of electron beams accelerated in the collisional plasma of solar (stellar) flares is considered. The stationary ion-acoustic turbulent mode localized at the magnetic looptop and magnetic fluctuations are taken into account. The astrophysical aspect of the propagation process is related to the interpretation of hard X-rays in the plasma of flare loops. For the plasma density in the solar flare looptop not exceeding 10¹⁰ cm^–3 and the ion-acoustic mode with the energy density to the thermal energy of the plasma ~5 × 10^–5–10^–3 and magnetic fluctuations with a level of 5 × 10^–2 the bright hard X-ray source in the looptop does not appear in the model of the isotropic pitch-angle distribution of accelerated electrons. In the anisotropic electron injection with a hard energy spectrum and ion-acoustic turbulence, the coronal hard X-ray source can exist for a short time after the turbulence generation starts. And only in the case of a soft energy spectrum of accelerated electrons (power spectrum index >5) and a high plasma density at the magnetic looptop >10¹⁰ cm^–3, a bright coronal hard X-ray source is generated at energies of 25–50 keV for any pitch-angular distribution of accelerated electrons at the injection time. A significant effect of turbulence on the distribution of the linear degree of hard X-ray polarization along the loop is shown, leading to a decrease in the extreme values in the coronal part by 5–35%. The integral values of the hard X-ray polarization do not exceed 10%.