We investigate the relationship between the continuum enhancement and the hard X-ray ( HXR ) emission of a white-light flare on 2002 September 29 .
By reconstructing the \it RHESSI HXR images in the impulsive phase , we find two bright conjugate footpoints ( FPs ) on the two sides of the magnetic neutral line .
Using the thick-target model and assuming a low-energy cutoff of 20 keV , the energy fluxes of non-thermal electron beams bombarding FPs A and B are estimated to be 1.0 \times 10 ^ { 10 } and 0.8 \times 10 ^ { 10 } ergs cm ^ { -2 } s ^ { -1 } , respectively .
However , the continuum enhancement at the two FPs is not simply proportional to the electron beam flux .
The continuum emission at FP B is relatively strong with a maximum enhancement of \sim 8 % and correlates temporally well with the HXR profile ; however , that at FP A is less significant with an enhancement of only \sim 4 - 5 % , regardless of the relatively strong beam flux .
By carefully inspecting the H \alpha line profiles , we ascribe such a contrast to different atmospheric conditions at the two FPs .
The H \alpha line profile at FP B exhibits a relatively weak amplitude with a pronounced central reversal , while the profile at FP A is fairly strong without a visible central reversal .
This indicates that in the early impulsive phase of the flare , the local atmosphere at FP A has been appreciably heated and the coronal pressure is high enough to prevent most high-energy electrons from penetrating into the deeper atmosphere ; while at FP B , the atmosphere has not been fully heated , the electron beam can effectively heat the chromosphere and produce the observed continuum enhancement via the radiative backwarming effect .