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BL Lacs are one subclass of blazars with highly energetic γ -ray emission, which is strongly boosted by a relativistic beaming effect. The latest catalogue of the 10 years of Fermi/LAT data (Abdollahi et al. 2020) and the γ -ray Doppler factors in Pei et al. (2020) provide us with a large BL Lac sample to study their jet emission morphologies and intrinsic properties. In this paper, we collected a sample of 294 Fermi BL Lacs and probed the correlations between the γ -ray emissions and luminosity distances. Our analyses give following conclusions: (1) the observed γ -ray emissions are really boosted by the γ -ray Doppler factor, and the intrinsic γ -ray emissions are closely correlated with luminosity distances. (2) the morphology of jet emissions for HBLs may be continuous, while that for IBLs may be the case of a moving sphere in the γ -ray bands. [ABSTRACT FROM AUTHOR]

Within a monitored duration of more than 7 yr, we obtained 1358 pairs of gri observations (514 at the g band, 393 at the r band, and 451 at the i band) for PKS0735+178 with a 1.26 m telescope in 20 nights from 2015 February 24 to 2016 April 28, and 98 VRI observations (27 at the V band, 35 at the R band, and 36 at the I band) with a 1.56 m telescope in 8 nights from 2009 January 13 to 2014 March 17. Based on the observations and analyses, we obtained the following results. (1) The maximum variation was 2.69 mag at the g band, and the largest intraday variations were Δmg = 0.89 ± 0.08 mag at the g band, Δmr = 0.38 ± 0.04 mag at the r band, and Δmi = 0.78 ± 0.15 mag at the i band. (2) We analyzed the intraday observations and find intraday optical variabilities with minimum timescales of ΔTg = 10.08 minutes, ΔTr = 10.08 minutes, and ΔTi = 10.08 minutes. (3) The variability rates of the magnitudes with time were consistent at three bands not only in the dimming stages but also in the brightening stages. (4) On 2016 January 19, we found intraday periodic oscillations, with a period P = 66.9 ± 4.1 minutes, based on which we calculated the mass to be in the approximate range of 1.5 × 107M⊙ to ∼8.9 × 107M⊙. (5) Based on our data and observations from the literature, we built long-term lightcurves of more than 100 yr and obtained two quasi-periods of P = 0.9 ± 0.4 yr and 12.4 ± 0.6 yr. [ABSTRACT FROM AUTHOR]

We analysed the multiband optical behaviour of the BL Lacertae object, S5 0716+714, during its outburst state from 2014 November to 2015 March. We took data on 23 nights at three observatories, one in India and two in Bulgaria, making quasi-simultaneous observations in B, V, R, and I bands. We measured multiband optical fluxes, colour, and spectral variations for this blazar on intraday and short time-scales. The source was in a flaring state during the period analysed and displayed intense variability in all wavelengths. R-band magnitude of 11.6 was attained by the target on 2015 January 18, which is the brightest value ever recorded for S5 0716+714. The discrete correlation function method yielded good correlation between the bands with no measurable time lags, implying that radiation in these bands originate from the same region and by the same mechanism. We also used the structure function technique to look for characteristic time-scales in the light curves. During the times of rapid variability, no evidence for the source to display spectral changes with magnitude was found on either of the time-scales. The amplitude of variations tends to increase with increasing frequency with a maximum of ~22 per cent seen during flaring states in B band. A mild trend of larger variability amplitude as the source brightens was also found. We found the duty cycle of our source during the analysed period to be ~90 per cent. We also investigated the optical spectral energy distribution of S5 0716+714 using B, V, R, and I data points for 21 nights. We briefly discuss physical mechanisms most likely responsible for its flux and spectral variations. [ABSTRACT FROM AUTHOR]

In this work, spectral energy distribution has been calculated for a sample of 597 Fermi blazars. Based on the calculation, we proposed a classification for subclasses of blazars as lower synchrotron peak sources (LSPs) if , intermediate synchrotron peak sources (ISPs) if , higher synchrotron peak sources (HSPs) if , ultra higher synchrotron peak sources (UHSPs) if . -ray luminosity is found correlated with lower energetic wavebands (radio, optical and X-rays). When redshift effect is removed, correlations are still strong for FSRQs; As for BL lacertaes, correlation between -ray and radio or between -ray and optical band is strong, but that between -ray and X-ray is only marginal. [ABSTRACT FROM AUTHOR]

In this talk, we will show the beaming effect for Fermi/LAT blazars, then we discuss the correlations between γ-ray luminosity and other parameters, such as radio Doppler factors, superluminal motions, and core-dominance parameters. We also compare the Doppler factors determined from the γ-ray luminosity, X-ray emissions, and the short-term time scales with those from other methods. Our discussions suggest that γ-ray emissions may be strongly beamed. [ABSTRACT FROM PUBLISHER]

The most identified sources observed by Fermi/LAT are blazars, based on which we can investigate the emission mechanisms and beaming effect in the γ-ray bands for blazars. Here, we used the compiled around 450 Fermi blazars with the available X-ray observations to estimate their Doppler factors and compared them with the integral γ-ray luminosity in the range of 1-100 GeV. It is interesting that the integral γ-ray luminosity is closely correlated with the estimated Doppler factor, νγLνγ = (2.95 ± 0.09)log δ + 43.59 ± 0.08 for the whole sample. When the dependence of the correlation between them and the X-ray luminosity is removed, the correlation is still strong, which suggests that the γ-ray emissions are strongly beamed. [ABSTRACT FROM AUTHOR]

In this paper, a sample of 451 blazars (193 flat spectrum radio quasars (FSRQs), 258 BL Lacertae objects) with corresponding X-ray and Fermi γ-ray data is compiled to investigate the correlation both between the X-ray spectral index and the γ-ray spectral index and between the spectral index and the luminosity, and to compare the spectral indexes αX, αγ, αXγ, and αγXγ for different subclasses. We also investigated the correlation between the X-ray and the γ-ray luminosity. The following results have been obtained. (1) Our analysis indicates that an anti-correlation exists between the X-ray and the γ-ray spectral indexes for the whole sample. However, when we considered the subclasses of blazars (FSRQs, the low-peaked BL Lacertae objects (LBLs) and the high-peaked BL Lacertae objects (HBLs)) separately, there is not a clear relationship for each subclass. For the average values, , we have ; and (2) For the correlations between the X-ray and the γ-ray luminosities, we have log νLγ = (1.033 ± 0.002)log νLX + (0.213 ± 0.094) for the whole sample, log νLγ = (0.741 ± 0.004)log νLX + (12.378 ± 0.162) for HBLs, and log νLγ = (1.032 ± 0.003)log νLX + (0.643 ± 0.138) for the LBLs and FSRQs; the correlation slope for HBLs is different from that for FSRQs and LBLs. For the average values, , we have , , and for the X-ray luminosity; and , , and for the γ-ray luminosity. (3) There is an anti-correlation between the effective spectral index, αXγ, and log νLγ for the whole sample, and the subclasses (FSRQs, LBLs, and HBLs). The effective spectral index shows that (4) For the spectral index difference, αγXγ(=αXγ – αγ) of the effective spectral index, αXγ, and the γ-ray spectral index, αγ, we obtain (5) Based on the Fermi-detected sources, we can say that the HBLs are different from FSRQs, while the LBLs are similar to FSRQs. [ABSTRACT FROM AUTHOR]