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Fig. 5

image

Left panel: stacked spectrum of the ten QSOs with 5.7 z 6.1 fit with a power-law model. On the bottom we report the residuals (datamodel). For clarity we adopted a minimum binning of ten counts per bin. Right panel: photon index vs. redshift. Black, green, and magenta points are the results of the Just et al (2007), Vignali et al. (2005), and Shemmer et al. (2006) stacking analyses, respectively. The blue point is the photon index of the stacked spectrum shown in the left panel. In all cases the assumed model is a simple power-law and errors are reported at the 68% confidence level.

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