Footpoint Motion of the Continuum Emission in the 2002 September 30 White‐Light Flare

We present observations of the 2002 September 30 white-light flare, in whichthe optical continuum emission near the Halpha line is enhanced by ~10%. Thecontinuum emission exhibits a close temporal and spatial coincidence with thehard X-ray (HXR) footpoint observed by RHESSI. We find a systematic motion ofthe flare footpoint seen in the continuum emission; the motion history followsroughly that of the HXR source. This gives strong evidence the this white-lightflare is powered by heating of nonthermal electrons. We note that the HXRspectrum in 10-50 keV is quite soft with gamma being ~7 and there is no HXRemission above 50 keV. The magnetic configuration of the flaring region impliesmagnetic reconnection taking place at a relatively low altitude during theflare. Despite a very soft spectrum of the electron beam, its energy content isstill sufficient to produce the heating in the lower atmosphere where thecontinuum emission originates. This white-light flare highlights the importanceof radiative backwarming to transport the energy below when direct heating bybeam electrons is obviously impossible.Comment: 16 pages, 5 figures, accepted for publication in Ap