Chromospheric Density Structures in Asymmetric Hard X-ray Footpoints of Flaring Loops

Hard X-ray (HXR) emission in conjugate footpoints of flaring loops is often asymmetric, which could be interpreted by the asymmetry of chromospheric density distribution in the overlaying magnetic loop. In a denser loop, more flare-produced energetic electrons can be stopped via collision with ambient plasma, which results in less non-thermal electrons reaching the chromosphere and thus weaker HXR emission observed in one footpoint. Based on RHESSI HXR observations, the source size of HXR footpoints and the height dependence of HXR emission energy can be achieved by using X-ray visibility forward fitting technique. Subsequently, the chromospheric density profile of a flaring loop will be constructed. Several specific limb flares with well-identified two HXR footpoints will be analyzed in this study. The variation of such density profile in different flaring periods will also be discussed.