Time structure and energy spectrum evolution of the solar flare x-rays measured by the «IRIS» spectrometer on board the «Coronas-f» spacecraft

The time structure and energy spectrum evolution of the X-ray emission of solar flares observed by spectrometer IRIS aboard the CORONAS-F spacecraft are investigated. It was found that the quasi-periodic oscillations from 10 to 30 s arise in the soft X-ray flare emission, while they are absent in the pre-flare one. The variation in the energetic spectrum of the hard X-ray emission of C-class flares was shown to depend on the distribution function of accelerated electrons.