  White-light (WL) flares have been observed and studied more than a century
since the first discovery. However, some fundamental physics behind the
brilliant emission remains highly controversial. One of the important facts in
addressing the flare energetics is the spatialtemporal correlation between the
white-light emission and the hard X-ray radiation, presumably suggesting that
the energetic electrons are the energy sources. In this study, we present a
statistical analysis of 25 strong flares (?greater than or equal to M5)
observed simultaneously by the Helioseismic and Magnetic Imager (HMI) on board
the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI). Among these events, WL emission was detected by
SDO/HMI in 13 flares, associated with HXR emission. To quantitatively describe
the strength of WL emission, equivalent area (EA) is defined as the integrated
contrast enhancement over the entire flaring area. Our results show that the
equivalent area is inversely proportional to the HXR power index, indicating
that stronger WL emission tends to be associated with larger population of high
energy electrons. However, no obvious correlation is found between WL emission
and flux of non-thermal electrons at 50 keV. For the other group of 13 flares
without detectable WL emission, the HXR spectra are softer (larger power index)
than those flares with WL emission, especially for the X-class flares in this
group.
