solar bursts were detected were excluded from analysis. Since such bursts are rather short-lived, the total duration of the time intervals rejected in this way in Prognoz 9 experiment was short, no longer than 0.3$\%$ of the total exposure time, for example, for the observations of the Galactic-Centre region. During the OS “Mir” GRIF experiment solar X-ray bursts were not detected at all because of the low solar activity during that time (1995-1997) [@Cof01].

To remove those variations in the Prognoz 9 experiment outputs which are correlated with the variations of the charged particle fluxes the regression analysis of the count rates in the X-ray channels ($N_x$) and in the charged-particle channel ($N_z$) was used. The relation between the count rate in a given X-ray channel and the count rate of charged particles detected by the anticoincidence cap can be assumed to be linear. Thus, the initial count rates in the analyzed time series can be represented as a superposition of the count rates that characterize the photon flux $\sim N_{x}^*$ under study and the additional count rates due to the charged particles ($\alpha N_z$): $$N_x = N_{x}^{*} + \alpha N_{z}.$$ The linear regression coefficients $\alpha$ were determined from the 