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We present a new method to fit the variations of both coordinates of a VLBI component as a function of time, assuming that the nucleus of the radio source contains a binary black hole system (BBH system). The presence of a BBH system produces 2 perturbations of the trajectory of the ejected VLBI components. By using only the VLBI coordinates, the problem we have to solve reduces to an astrometric problem. Knowledge of the variations of the VLBI coordinates as a function of time contains the kinematical information, thus we are able to deduce the inclination angle of the source and the bulk Lorentz factor of the ejected component. Generally, there is a family of the BBH system producing the same fit to our data. To illustrate this method, we apply it to the source 1807+784. We find that the inclination of the source is i = 5.8+-1.8 degrees and the VLBI component is ejected with a bulk Lorentz factor of 3.7+-0.3. We determine the family of the BBH system which provides the best fit, assuming at first that the masses of the 2 black holes are equal and then that the masses are different. Each family of BBH systems is characterized by Tp/Tb~1.967, where Tp and Tb are the precession period of the accretion disk of the black hole ejecting the VLBI component and the orbiting period of the BBH system.
We present the results of a multi-frequency analysis of the structural variability in the parsec-scale jet of the blazar S5 1803+784. More than 90 epochs of observations at 6 frequencies from 1.6 GHz up to 22 GHz have been combined and analyzed. We d
The radio, optical, and $gamma$-ray light curves of the blazar S5 1803+784, from the beginning of the {it Fermi} Large Area Telescope (LAT) mission in August 2008 until December 2018, are presented. The aim of this work is to look for correlations am
To determine the location of the intra-day variable (IDV) emission region within the jet of the BL Lac object S5 0716+714, a multi-epoch VSOP polarization experiment was performed in Autumn 2000. To detect, image, and monitor the short term variabili
Using the 1.56m telescope at the Shanghai Observatory (ShAO), China, we monitored two sources, BL Lac object S5 0716+714 and Flat Spectrum Radio Quasar (FSRQ) 3C 273. For S5 0716+714, we report 4969 sets of CCD (Charge-coupled Device) photometrical o
High signal-to-noise spectroscopy has established a redshift of z=0.494 for the source 2QZJ215454.3-305654, originally selected from the 2dF/6dF QSO Redshift Surveys as one of 45 candidate BL Lac objects displaying a featureless continuum at optical