Raw light curve of GRB 221009A as observed by GRBAlpha in multiple energy bands with 4 s cadence. The bottom-rightmost panel shows the light curve in the whole sensitivity range. Times t_b, t_s, and t_p mark the beginning of the used background interval, the source spectral data, and the peak time, respectively. About 30 s after the peak at t_p, the GRB shows a second strong peak. Time t_r marks the approximate moment when the satellite entered the outer Van Allen radiation belt, which resulted in the final part of the GRB prompt emission being flooded by the particle background. The sharp increase just after t_r is due to this background.