Fraction of the detected counts in each spectral band vs the total counts over the whole energy range for GRB 221009A and for the background as it passed the north polar region. The counts were detected in 4 s time bins. The figure shows that above ∼10 000 cnt bin = 2500 cnt s⁻¹ the fraction of counts in low-energy bands decreases while the fraction of counts in high-energy bands increases, which can indicate a pile-up effect.