White-light Emission and Chromospheric Response by an X1.8-class Flare on 2012 October 23

On 2012 October 23, a strong white-light emission, associated with an X1.8-class flare, was observed by the Solar Optical Telescope on board the Hinode satellite. White-light kernels were clearly observed along the Ca ii H ribbons. RHESSI also observed hard X-ray emissions that were almost located on the white-light kernels. The total energy of the white-light emission was $\sim {10}^{27-28}erg{s}^{-1}$ and the total energy of the accelerated electrons was almost of the same order when we used 40 keV as the lower energy cutoff. The white-light emission appears to have originated from nonthermal electrons in these energies. Moreover, the EUV imaging spectrometer on board the Hinode satellite performed a raster scan over this flaring active region and the flare occurred during the scan. Over the white-light kernels, we observed redshifts of a few tens of km s⁻¹ in Fe xii. It appears that these EUV responses originated from some accelerated electrons due to the solar flare and they are considered to be the source of the white-light emission. In fact, the electron density of the white-light kernels was less than ${10}^{12}{cm}^{-3}$, which is sufficiently low for nonthermal electrons to penetrate into the photosphere.