High Resolution Imaging of Solar Flare Footpoints in White Light and Hard X-rays

We test the standard thick target beam scenario of solar flares using high resolution G-band (430 nm) observations (~0.2 arcsec) taken by HINODE/SOT and hard X-ray observations (2.3 arcsec) from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) of the December 6, 2006 GOES X9 flare. At both wavelengths, several co-spatial footpoint sources are seen on the flare ribbons that show similar relative intensities. This excellent correlation suggests that the suprathermal electrons producing the hard X-ray emission are also the source of energy for the white light emission, excluding energetic protons as a possible source. If both emissions indeed come from the same location, the higher resolution G-band observations suggest that the individual hard X-ray sources are unresolved. Using the footpoint area from the G-band images, the energy deposition rate by the hard X-ray producing electron beam in cold thick target approximation become enormous with values of 2x10 12 erg/s/cm2 for 25 keV (9x1012 erg/s/cm2 for 10 keV). This corresponds to a giant electron beam density within the hard X-ray source of 0.3x1010 cm-3 above 25 keV (5x1010 cm-3 above 10 keV). These estimates pose serious questions for the thick-target beam interpretation. We will discuss alternative scenarios, including the idea of a purely non-thermal electron distribution as the source of the hard X-ray emission.