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Since the Fermi Large Area Telescope launch, a large sample of blazars has been detected in the γ -ray band. One of the important parameters, the variability index (VI), is adopted to quantify the γ -ray blazar variability. The variability of blazars can be affected by the geometric jet structure, accretions, source sizes, or evolutions of particles. In this paper, we compiled a sample of 2250 blazars (792 flat spectrum radio quasars, 1458 BL Lacertae objects) with some physical parameters to investigate the correlations between the VI and beaming effects. The VI shows positive correlations with the Doppler factors, γ -ray luminosities, core dominances, and superluminal motions for both FSRQs and BL Lacs but only holds a positive correlation on polarizations for BL Lacs. The close correlations between VI and the beaming indicators reinforced the previous results that the γ -ray variability is related to the jet, and the VI can be regarded as an effective indicator for the jet beaming effects of Fermi blazars. [ABSTRACT FROM AUTHOR]

The blazar sequence, including negative correlations between radiative luminosity L rad and synchrotron peak frequency ν, and between Compton dominance Y and ν, is widely adopted as a phenomenological description of spectral energy distributions (SEDs) of blazars, although its underlying cause is hotly debated. In particular, these correlations turn positive after correcting Doppler boosting effect. In this work, we revisit the phenomenological and intrinsic blazar sequence with three samples, which are historical sample (SEDs are built with historical data), quasi-simultaneous sample (SEDs are built with quasi-simultaneous data) and Doppler factor corrected sample (a sample with available Doppler factors), selected from literature. We find that phenomenological blazar sequence holds in historical sample, but does not exist in quasi-simultaneous sample, and intrinsic correlation between L rad and ν becomes positive in Doppler factor corrected sample. We also analyse if the blazar sequence still exists in subclasses of blazars, i.e. flat-spectrum radio quasars and BL Lacertae objects, with different values of Y. To interpret these correlations, we apply a simple scaling model, in which physical parameters of the dissipation region are connected to the location of the dissipation region. We find that the model generated results are highly sensitive to the chosen ranges and distributions of physical parameters. Therefore, we suggest that even though the simple scaling model can reproduce the blazar sequence under specific conditions that have been fine-tuned, such results may not have universal applicability. Further consideration of a more realistic emission model is expected. [ABSTRACT FROM AUTHOR]

In this work, the support vector machine (SVM) method is adopted to separate BL Lacertae objects (BL Lacs) and flat spectrum radio quasars (FSRQs) in the plots of the photon spectrum index against the photon flux, α ph ∼ log F , those of the photon spectrum index against the variability index, α ph ∼ log V I and those of the variability index against the photon flux, log V I ∼ log F . Then, we used the dividing lines to distinguish BL Lacs from FSRQs in the blazar candidates of uncertain types from the Fermi/LAT catalogue. Our main conclusions are: 1. We separate BL Lacs and FSRQs by α ph = − 0.123 log F + 1.170 in the α ph ∼ log F plot, α ph = − 0.161 log V I + 2.594 in the α ph ∼ log V I plot and log V I = 0.792 log F + 9.203 in the log V I ∼ log F plot. 2. We obtain 932 BL Lac candidates and possible BL Lac candidates, and 585 FSRQ candidates and possible FSRQ candidates. 3. Discussion is given regarding comparisons with the literature. [ABSTRACT FROM AUTHOR]

In this work, we collected a sample of BL Lacs and FR I and FR II(G) radio galaxies with available core and extended emissions from published works to discuss the unified schemes and estimate the Doppler factor for BL Lacs. A Wilcoxon rank-sum test and a Kolmogorov–Smirnov test both suggest that the probabilities of the distribution of the extended luminosity of BL Lacs and that of FR I and FR II(G) radio galaxies being from the same parent distribution are p WRS = 0.779 and p K-S = 0.326, suggesting they are unified. Based on this unified scheme, we propose to estimate the Doppler factors for BL Lacs. Comparing the Doppler factor estimated by the fitting/regression method with those for the common sources in the literature, we found a good linear correlation for common sources. [ABSTRACT FROM AUTHOR]

In a two-component jet model, the emissions are the sum of the core and extended emissions: $$S^{\mathrm{ob}}=S_{\mathrm{core}}^{\mathrm{ob}}+S_{\mathrm{ext}}^{\mathrm{ob}}$$ , with the core emissions, $$S_{\mathrm{core}}^{\mathrm{ob}}= f S_{\mathrm{ext}}^{\mathrm{ob}}\delta ^{q}$$ being a function of the Doppler factor $$\delta $$ , the extended emission $$S_{\mathrm{ext}}^{\mathrm{ob}}$$ , the jet type dependent factor q, and the ratio of the core to the extended emissions in the comoving frame, f. The f is an unobservable but important parameter. Following our previous work, we collect 65 blazars with available Doppler factor $$\delta $$ , superluminal velocity $$\beta _{\mathrm{app}}$$ , and core-dominance parameter, R, and calculated the ratio, f, and performed statistical analyses. We found that the ratio, f, in BL Lacs is on average larger than that in FSRQs. We suggest that the difference of the ratio f between FSRQs and BL Lacs is one of the possible reasons that cause the difference of other observed properties between them. We also find some significant correlations between $$\log f$$ and other parameters, including intrinsic (de-beamed) peak frequency, $$\log \nu _{\mathrm{p}}^{\mathrm{in}}$$ , intrinsic polarization, $$\log P^{\mathrm{in}}$$ , and core-dominance parameter, $$\log R$$ , for the whole sample. In addition, we show that the ratio, f, can be estimated by R. [ABSTRACT FROM AUTHOR]