Differential number counts in the 0.5−2 keV band normalized to the Euclidean slope. The data points and the dotted line are taken from Georgakakis et al. (2008); dot-dash curve shows the AGN model by Ueda et al. (2003); solid lines – the number counts estimates based on the NNST in the AEGIS field: thick solid line – the best power-law fit, thin solid lines – 1σ uncertainty range due to the counting statistics; dashed lines – maximum total uncertainty including potential errors generated by inaccuracies in the PSF fitting. The count normalization at the bright end of the NNST model is fixed at the amplitude given by the Georgakakis et al. (2008) approximation.