The 2017 September 10 loop-prominence system: A polarization and density analysis

Abstract:

Classical loop-prominence systems associated with powerful solar flares have been observed since the 1930’s. Since their initial observations, loop prominence systems (LPS) were a topic of particular interest for solar physicists as they seem to have a clear relationship with solar flares. The time evolution of loop prominence systems is related to the thermodynamic and radiative properties of the chromospheric plasma. From observations it is clear that these systems do not grow from lower to higher altitudes, instead their generation is the product of higher loops getting more intense, while the lower decay. Here, we report observations of white-light ejecta in the low corona after the 2017 September 10 flare, using data from the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory. We interpret this as a classical loop-prominence system, but find it to be brighter than expected and possibly seen here in the continuum rather than line emission. We studied the spatial and temporal relation between RHESSI X-ray and the white-light emissions at altitudes, where the polarization levels detected match well those expected from pure Thomson scattering by the coronal material. We also studied the HMI spectroscopic data to determine the most probable emission mechanism that can explain the observation of the loop-prominence system.