Context :

Aims : The H \alpha emission of solar flare kernels and associated hard X-ray ( HXR ) emission often show similar time variations but their light curves are shifted in time by energy transfer mechanisms .
We searched for fast radiative response of the chromosphere in the H \alpha line as a signature of electron beam heating .

Methods : We investigate the time differences with sub-second resolution between the H \alpha line emission observed with a Multi-channel Subtractive Double Pass ( MSDP ) spectrograph on the Large Coronagraph and Horizontal Telescope at Białków Observatory , Poland , and HXR emission recorded by the RHESSI spacecraft during several flares , greatly extending our earlier analysis ( Paper I ) to flares between 2003 and 2005 .

Results : For 16 H \alpha flaring kernels , observed in 12 solar flares , we made 72 measurements of time delays between local maxima of the RHESSI X-ray and H \alpha emissions .
For most kernels , there is an excellent correlation between time variations in the H \alpha line emission ( at line centre and in the line wings ) and HXR ( 20–50 keV ) flux , with the H \alpha emission following features in the HXR light curves generally by a short time lapse \Delta t = 1 –2 s , sometimes significantly longer ( 10–18 s ) .
We also found a strong spatial correlation .

Conclusions : Owing to our larger number of time measurements than in previous studies , the distribution of \Delta t values shows a much clearer pattern , with many examples of short ( 1–2 s ) delays of the H \alpha emission , but with some flares showing longer ( 10–18 s ) delays .
The former are consistent with energy transfer along the flaring loop legs by non-thermal electron beams , the latter to the passage of conduction fronts .