Our team highlighted the pion-decay component during the impulsive phase of August 25, 2001, October 28, 2003, November 4, 2003, and January 20, 2005, powerful flares as well as appearance of neutron fluxes after the first three events.
The impulsive phase of the August 25, 2001, solar flare (GOES X5.3/3B, S17E34) was characterized by a gradual increase in the total intensity and energy of accelerated particles (see [38-41]).
According to measurements within various ranges, the beginning of the impulsive phase (the beginning of the main energy release of this flare) was determined as 11:01-11:02 (see, e.g., [45-47]).
Thus, 10 min of our measurements covered practically the total time interval of the flare impulsive phase except the very beginning of the event between 19:38:30 and 19:42:14.
We were lucky and have measured gamma-rays with energies up to 100-200 MeV when the impulsive phase of 4 powerful flares, namely, August 25, 2001, October 28, 2003, November 4, 2003, and January 20, 2005, was in progress.
It is known that at the beginning of the flare impulsive phase the value of [dI.sub.SXR]/dt does not exceed 20-30% of its peak value.
Kaufmann et al., "Analysis of the impulsive phase of a solar flare at sub millimeter wavelengths," Solar Physics, vol.
Yushkov et al., "Spectral peculiarities of high energy X-ray radiation, gamma radiation, and submillimeter radio emission in the impulsive phase of a solar flare," Bulletin of the Russian Academy of Sciences, Physics, vol.