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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]

3C 273 is a well-studied FSRQ. In order to analyze its spectrum variabilities, we make spectroscopic observations of 3C 273 using the 2.16 m telescope at Xinglong Observatory of the National Astronomical Observatories. Based on these observations and some other spectra from the literature, we study the spectrum variabilities and the physical origin of the optical spectrum. The main results are as follows: (1) The continuum spectrum (S c ) shows obvious variabilities and displays quasi-periodic properties, P = 3.39 ± 1.13 yr, consistent with the result calculated from photometric observations. (2) The spectral energy distribution (SED) was modeled by a combination of blackbody emission that originated from the accretion disk and the dusty torus, synchrotron emission from the jet, the synchrotron self-Compton (SSC) emission, and the external Compton (EC) emission from the broad-line region, accretion disk, and dusty torus. The SED suggests that the optical continuum is dominated by the thermal emission from the accretion disk. (3) A time delay of τ c H β = 209.42 ± 9.38 days lies between the slope of the continuum spectrum (S c ) and H β emission line. (4) The relationships between the spectrum and polarization can be explained by the jet model. [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]

Blazars show extreme observational properties that are due to the beaming effect with the jet being close to the line of sight. It was found that the observed luminosity is anticorrelated with the synchrotron peak frequency but the debeamed luminosity and the frequency is positively correlated. In this work, we revisit this correlation for a large sample of 255 blazars from the fourth Fermi catalog with available Doppler factors. Our analysis comes to the following conclusions. (1) The observed radio, X-ray, Îł -ray, and synchrotron peak luminosity are all anticorrelated with the peak frequency, but the debeamed luminosity is positively correlated with the debeamed peak frequency. The anticorrelation is due to a selection effect or a beaming effect. (2) The Compton dominance parameter is correlated with both the bolometric luminosity and Doppler factor, implying that the more highly Compton-dominated sources are more luminous. (3) The bolometric luminosity can be represented by the Îł -ray luminosity for Fermi blazars. [ABSTRACT FROM AUTHOR]