The multi-wavelength study of the effect of energetic particle beams on the chromospheric emission in the 25th July 2004 solar flare Original Research Article

We present the multi-wavelength study of short-term variations of Hα line emission located in multiple kernels on the both sides from magnetic neutral line in the 25th July 2004 solar flare observed by VTT (Tenerife). The HXR and Hα emission in the kernels 1 and 3 is close spatially and temporally while in kernels 4 and 7 there is only delayed Hα emission observed tens seconds after HXR in the kernels 1 and 3. The locations of Hα kernels 1, 3, 4 and 7 are on the opposite sides from the magnetic neutral line. The temporal variations of Hα emission in kernels 1 and 3 coincide within 5 s with the HXR photon emission. The latter is found to have double power law photon spectra, which were corrected to a single power law with the turning point technique accounting for Ohmic losses and collisions. The Hα emission is fit by full non-LTE simulations in an atmosphere heated by an electron beam with the parameters derived from the HXR emission. The combination of radiative, thermal and non-thermal mechanisms of excitation and ionization of hydrogen atoms is considered. The temporal evolution of simulated Hα emission in the kernel 3 fits rather well the two observed intensity increases: the first at the flare onset (13:38:39–13:39:30 UT) caused by pure non-thermal excitation by beam electrons and the second one appearing after 13:40:00 UT because of a hydrodynamic heating. The observed close temporal correlation or delay of Hα emission with HXR emission points out to the precipitation either of electron (kernels 1 and 3) or protons (4 and 7).