Gamma-ray radiation properties of Fermi blazars

To understand the radiation mechanism of blazars’ high-energy γ-ray, the relationship between the change in γ-ray photon spectral index (ΔΓ) and luminosity change (ΔlogL) among adjacent source catalogs in Fermi/LAT 1FGL, 2FGL, 3FGL, 4FGL, 4FGL-DR2, 4FGL-DR3, and 4FGL-DR4 was studied. The results indicate: (1) As the γ-ray radiation frequency increases, the γ-ray brightness of FSRQs and LBLs gradually decreases, while the brightness of HBLs shows an increasing trend, and the brightness of BL Lacs remains relatively constant. (2) With the increase in γ-ray radiation frequency, the correlation between ΔlogL and ΔΓ changes from positive to negative. For different sub-class samples of blazars, the transition energy (ET) at which this correlation changes from positive to negative varies, and ET, BL Lacs >ET, FSRQs. (3) For a sub-class sample of blazars, when their γ-ray radiation energy is below the transition energy, the source becomes dimmer as its spectrum flattens; when above the transition energy, the source becomes brighter as its spectrum flattens. (4) Below the transition energy, γ-ray radiation is dominated by the synchrotron self-Compton (SSC) mechanism, while above the transition energy, it is dominated by the external Compton (EC) mechanism. Therefore, BL Lac γ-ray radiation has more SSC components, whereas FSRQ has more EC components.