RHESSI Observations of Hard X-ray Footpoint Motions in Solar Flares

Solar HXR bremsstrahlung from energetic electrons accelerated in the impulsive phase of a flare is observed to be primarily from the footpoints of magnetic loops. Standard magnetic reconnection models predict increasing separation of the footpoints during the flare as longer and larger loops are produced. If the reconnection process results in accelerated electrons, the HXR footpoints should show this motion. The motion is only apparent; it is due to the HXR emission shifting to footpoints of neighboring newly reconnected field lines. The speed of footpoint separation reflects the rate of

magnetic reconnection and should be roughly proportional to the total energy deposition in the footpoints. We studied footpoint motions in several large flares with the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and compared the motion with the energy deposition rate in the footpoints. A correlation between the motion and the energy deposition rate is found during some periods in these flares, but not always.