A sample including 664 blazars （301 Flat Spectrum Radio Quasars and 363 BL Lacs） with ）γ-ray data in both 1FGL and 2FGL catalogues were selected. The average values of both y-photon average energy and the photon spectral index for FSRQs, LBLs, IBLs and HBLs, follow the blazars sequence, FSRQs → LBLs →IBLs → HBLs. The slopes of correlation between photon spectral index and ）,-ray luminosity for 4 the sub-classes of blazars also follow the blazars sequence. Also, there was close an- ti-correlations between the difference of two ）,-ray photon spectral indices and the logarithm of the ratio of two y-ray luminosities from 2FGL and 1FGL catalogs. It implies that the spectrum becomes flat when the source becomes brighter in high energetic γ-ray band. Lastly, the Kolmogolov-Smirnov test （KS test） of the average γ-photon energy showed that HBLs differs from LBLs and FSRQs, while there was no clear difference between LBLs and FSRQs, which implied that the γ-ray emissions in LBLs and FSRQs may be a result of the same emission mechanism.
In this paper, the preliminary data from University of Michigan Radio Astronomy Observatory database （UMRAO） are used to discuss the radio spectral index properties of 8 BL Lacs. To do so, we calculated the radio spectral index, a （F oc va）, which was obtained by fitting the averaged flux densities in the bands （4.8 GHZ, 8 GHz, and 14.5 GHz） by binning the original for 7 d. We also calculated the time delay between the averaged lightcurves and the spectral variance. Our calculations and analysis give the following results. 1） The averaged logarithmic flux density at 8 GHz （logF） and the corresponding spectral index （or） have strong correlation for all the BL Lacs; 2） the lightcurves and the spectral variability have the similar profile for all the BL Lacs; 3） the lightcurves delay spectral variability for all sources but PKS 0735＋178, with the delay time ranging from 31 d to 125 d.
In this paper, a sample including 68 blazars (18 BL Lacs and 50 FSRQs) with known Doppler factors and superluminal velocity from our previous papers is presented. Both the Lorentz factors (/') and viewing angles (0) are estimated for the 68 sources The relationship between BL Lacs and FSRQs is also revisited using the two variables off'and 0. The Lorenz factors are in the range of 2.33 to 64.07. The viewing angles are in the range of 0.04 to 24.56. The averaged value of the viewing angle for BL Lacs is slightly larger than that for FSRQs, while the averaged value of the Lorentz factor for BL Lacs is smaller than that for FSRQs.
In this paper, we revisit the relationship between the spectral index and the core-dominance parameter using a larger sample of 157 blazars (23 BL Lacertae objects and 134 flat spectrum radio quasars), compiled from the available literature. From the relevant data, we find the spectral index associated with the core-dominance parameter, for which a relativistic beaming effect is responsible. In addition, we make a comparison of the properties between BL Lacertae objects and flat spectrum radio quasars.
Based upon Fermi 1FGL and EGRET 3EG samples, a sample including 79 blazars （53 FSRQs, 26 BL Lacs） is presented. It is investigated that the correlations between the ratio of EGRET to Fermi blazars g-ray flux densities and the spectral index differ for EGRET to Fermi blazars for three subclasses of high-frequency peaked BL Lacertae objects-HBL, low-frequency peaked BL Lacertae objects-LBL, and flat spectrum radio quasars-FSRQs. There is a consistent relationship between the ratio of the two γ-ray flux densities and the spectral index difference for the three subclasses. It suggests that the spectrum changed with the source brightness in the gamma-ray band. Both the spectral index difference and the correlation slopes follow a continuous sequence from FSRQs to LBLs to HBLs, which is consistent with the noted blazar sequence.
S5 0716＋714 is one of the targets in our long term blazar monitoring program carried out with the 1.56-m telescope at Sheshan Station of Shanghai Astronomical Observatory, China. We report a very rapid variability of △I=0.611±0.102 mag over 3.6 min detected in our monitoring program during the period from December 2000 to March 2007. The rapid variability suggests that the mass for the central black hole is log（M/M⊙） = 7.68 - 8.38.
Active galactic nuclei （AGNs） have two major classes, namely radio loud AGNs and radio quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which display extreme observational properties, such as rapid variability, high luminosity, high and variable polarization, and superluminal motion. All of those observational properties are probably due to a relativistic beaming effect with the jet pointing close to the line of sight. Observations suggest that the orientation can be expressed by a core-dominance parameter, R. The R, to some extent, is associated with the beaming effect. Blazars are believed to be unified with Fanaroff ＆ Riley type I/II （FRI/II） radio galaxies. In this work, we collected relevant observations from the literature for a sample of 1223 AGNs including 77 BL Lacertae objects, 495 quasars, 460 galaxies, 119 FRs and 72 unidentified sources, and calculated the core-dominance parameters and spectral indexes, discussed the relationship between the two parameters, and gave some discussions. Our analysis suggests that the core-dominance parameters in BL Lacertae objects are larger than those in quasars and galaxies, and the radio spectral indexes in BL Lacertae objects are lower than those in quasars and galaxies. We also found that the core-dominance parameter-spectral index correlation exists for a large sample presented in this work, which may come from a relativistic beaming effect.
