Scaling of the photon index Γ vs. the normalization N_BMC for M 87 (black line – target source) using Galactic sources: XTE J1550–564, 4U 1630–472 and H 1743–322 (reference sources). Pink crosses stand for RXTE data of 4U 1630–472, green circles mark H 1743–322 data, and blue squares indicate XTE J1550–564 data. Pink dashed line indicates the Γ-Norm correlation corrected for a nucleus emission from M 87 using Chandra data (pink points). For the scaling of a BH mass of M 87 we used this corrected Γ-Norm track (see details in the text).