Power-law index of VHE spectra as a function of the VHE flux above 300 GeV measured by MAGIC. The photon index values, which are not corrected for EBL absorption, are listed in Table 2. The color scheme is the same as the one used in Fig. 2 and in Fig. 3. In addition, the result for the multi-wavelength campaign is shown in blue, and the historical measurements from Aleksić et al. (2014a) are shown in black. The solid and dashed lines represent a constant and a linear fit, respectively.