In this work, we exploit the luminosity of the broad-line region (BLR) for 50 Fermi blazars through matching the coordinates between the Sloan Digital Sky Survey catalog, Fermi Large Area Telescope Third Source Catalog, and the Fermi Large Area Telescope Fourth Source Catalog and fitting their emission lines. In total, we collected a sample of 350 blazars with broad-line emissions including 50 new objects and 300 blazars from published works to revisit the correlation between the γ-ray luminosity and the broad-line luminosity, and proposed a new method to estimate the Doppler factors based on the correlation between the radiative power of the jet and luminosity of the BLR. We come to following conclusions. (1) For the 50 Fermi blazars, their broad-line luminosity (log L _BLR) ranges from 41.82–45.2 erg s⁻¹ with a mean value of 44.39 erg s⁻¹. (2) The Doppler factor (δ) ranges from δ = 0.35 to δ = 85.66 with a mean value of 12.54, which is consistent with the results in the literature. (3) There are positive correlations between γ-ray luminosity and broad-line luminosity, and between γ-ray luminosity and the Doppler factor.

The origin of jets is one of the most important issues concerning active galactic nuclei, yet it has remained obscure. In this work, we made use of information from emission lines, spectral energy distributions, and Fermi–LAT γ-ray emission to construct a blazar sample that contains 667 sources. We note that jet power originations are different for BL Lacertae objects (BL Lacs) and flat-spectrum radio quasars (FSRQs). The correlation between jet power P _jet and the normalized disk luminosity L _Disk/L _Edd shows a slope of −1.77 for BL Lacs and a slope of 1.16 for FSRQs. The results seem to suggest that BL Lac jets are powered by extracting black hole (BH) rotation energy, while FSRQ jets are mostly powered by accretion disks. Meanwhile, we find the accretion ratio M ̇ / M ̇ Edd increases with the normalized γ-ray luminosity. Based on this, we propose a dividing line, log ( L BLR / L Edd ) = 0.25 log ( L γ / L Edd ) − 2.23 , to separate FSRQs and BL Lacs in the diagram of L _BLR/L _Edd against L _γ /L _Edd using a machine-learning method; the method gives an accuracy of 84.5%. In addition, we propose an empirical formula, M BH / M ☉ ≃ L γ 0.65 / 21.46 , to estimate BH mass based on a strong correlation between γ-ray luminosity and BH mass. Strong γ-ray emission is typical in blazars, and the emission is always boosted by a Doppler-beaming effect. In this work, we generate a new method to estimate a lower limit of Doppler factor δ and give δ _{BL Lac} = 7.94 and δ _FSRQ = 11.55.

Studies and constraints on the emission region are crucial to the blazar radiation mechanism. Yet previous works have mainly focused on individual sources. In this work, we make use of the largest and the latest spectral energy distribution fitting results in the literature to statistically study the blazar emission region properties in the framework of a one-zone leptonic model. Our results reveal: (1) that flat-spectrum radio quasars (FSRQs) show lower electron energy (γ _p ≲ 1.6 × 10³) than BL Lacertae objects (BL Lacs) and tend to have a stronger magnetic field (B) and smaller electron-to-magnetic energy ratio (U _e/U _B) than BL Lacs; (2) we find that the electromagnetic equipartition would rather happen in the jets of BL Lacs than happen in the jets of FSRQs; (3) there are 682 blazars with a magnetic field weaker than the critical value for generating the Kelvin–Helmholtz instability, thus one-third of the blazars in our sample are able to produce this instability; and (4) the distance (d _em) between the emission region and the central black hole is on the scale of ∼0.1 pc, so the location of the emission region may be evenly distributed inside and outside the broad-line region.

It is known that the blazar jet emissions are dominated by nonthermal radiation, while the accretion disk jets are normally dominated by thermal emission. In this work, our aim is to study the connection between the two types of emission by investigating the correlation between the blazar emission-line intensity property, which embodies the nature of an accretion disk, and the γ-ray flux property, which is the representative of jet emission. We compiled a sample of 656 blazars with available emission-line equivalent widths (EWs), the GeV γ-ray flux, and the spectral energy distribution (SED) information from the literature. In this work, we found 55 previous blazar candidates of uncertain types (BCUs) that are now identified as flat-spectrum radio quasars (FSRQs), and found 52 “changing-look” blazars based on their EWs, 45 of which are newly confirmed. These changing-look blazars have a larger accretion ratio ( M ̇ / M ̇ Edd ) than BL Lacertae (BL Lac) objects. In addition, we suggest that the lower synchrotron peak blazars (LSPs) could be the source of changing-look blazars because 90.7% of the changing-look blazars in this work are confirmed as LSPs. An anticorrelation between EW and continuum intensity, the so-called global “Baldwin effect” (BEff), has been confirmed. We suggest that the steeper global BEff observed for the blazar than for radio-quiet active galactic nuclei (RQ-AGNs) is caused by the inverse Compton scattering of broad-emission-line photons. This interpretation is further supported by the positive correlation between the emission-line EW and intrinsic inverse Compton luminosity.

The study of blazar jet has been performed for several decades via VLBI technique, while its generation and propagation stay unclear. In the present work, we compiled a sample of 407 VLBI detected Fermi blazars (VFBs) and studied the correlations between apparent velocity (log β_app) and jet/accretion disk properties. We found a positive correlation between γ-ray luminosity (log L_γ) and log β_app, the correlation suggests that the apparent motion of jet knot is related to the jet power. The correlations between |${\rm log}\, \beta ^{\rm max}_{\rm app}$| and the jet radiation power (log L_rad) and between |${\rm log}\, \beta ^{\rm max}_{\rm app}$| and the jet extended region luminosity at 5 GHz (⁠|${\rm log}\, L_{\rm 5GHz}^{\rm ext}$|⁠), which is an indicator of jet kinetic power, reveal that the knots apparent motion is correlated with both jet radiation power and the kinetic power. But this indication is not held for FSRQs in terms of the correlation |${\rm log}\, L_{\rm 5GHz}^{\rm ext}\, versus \, {\rm log}\, \beta ^{\rm max}_{\rm app}$|⁠. Besides, |${\rm log}\, \beta ^{\rm max}_{\rm app}$| has a moderate correlation with accretion disk luminosity (log L_Disk) and the normalized accretion disk luminosity log (L_Disk/L_Edd), this may suggest both the power of accretion disk and the accretion rate are critical to generate knots and to accelerate them. In addition, we found the VFBs have larger average values of γ-ray luminosity (log L_γ), γ-ray photon index (α_ph), and variability index (log VI) than the rest of Fermi blazars. Through Gaussian mixture models method, we generated a criteria, log L_γ > 45.40, α_ph > 2.24 and log VI > 1.71 to find VFB candidates, selected 228 VFB candidates from the rest of Fermi blazar.