Left panel: X-ray photon index as a function of M_BH for the X-WISSH quasars with X-ray spectroscopy (filled stars indicate objects with a Hβ-based SMBH mass; Bischetti et al. 2017; Vietri et al., in prep.) and while open stars indicate sources with a CIV-based SMBH mass (Weedman et al. 2012). We also report data for other samples as follows: the cyan diamonds indicate intermediate M_BH AGN by Miniutti et al. (2009b) and Ludlam et al. (2015); the orange squares denote the AGN from Jin et al. (2012a); the magenta triangles and blue circles represent high-z quasars from Kelly et al. (2008) and Shemmer et al. (2008), respectively. The black dashed and solid lines represent the linear and broken power-law relations found in this work; the gray shaded area indicates the combined uncertainties in slope and normalization. The gray dashed line and the solid line indicate the linear and broken power law found by Jin et al. (2012a) and Kelly et al. (2008), respectively. Errors on Γ are consistently reported at 90% c.l. for all the sources. Right panel: binned Γ over the following log(M_BH/M_⊙) ranges: 5–7, 7–9, and 9–11.