The empirical basis of quasar astronomy can be overawing especially in the twenty-first century. A first source of intricacy involves the nomenclature that has evolved to label the multifold phenomenological manifestations now united under the umbrella of active galactic nuclei (AGNs). A further complication involves observations of the many subclasses with the observations now spanning the electromagnetic spectrum.

Quasars: The Observational Perspectives

A wavelet analysis method is introduced to study the possible periods of PKS 1510-089 in radio bands. By compiling the radio light curve of PKS 1510-089 at frequencies of 22 and 37 GHz from 1990 to 2005, and using the wavelet analysis method, the evidence of quasi-periodic activity in PKS 1510-089 was obtained. The results indicate that: (1) There are two stable outburst periods of T
 1=(1.80±0.06) yr and T
 2= (0.90±0.07) yr presenting in the isoplethal map of PKS 1510-089 at the radio band 37 GHz; (2) there is an outburst period of T
 1=(1.80±0.06) yr presenting at the radio band 22 GHz; (3) by the continuum of the isograms map, we find the primary period of PKS 1510-089 is T
 1=(1.80±0.06) yr, and the period of T
 2= (0.90±0.07) yr may be the half period. The above results are consistent with the reports of Xie et al. (2004, 2005, 2008), Wu et al. (2005) and Liu & Fan (2007), using the other methods. We can expect that the next burst will be in January 2011.

The characteristic periodicity analysis of the radio flux variability of quasar PKS 1510-089

The data from the last 60 years on the programs of long-term multi-frequency monitoring of active galactic nucleus (AGN) 3C 273 were analyzed. A model is proposed for finding the parameters of close binary systems (CBSs) from supermassive black holes (SMBHs), including a harmonic analysis of observational data series obtained in the optical and radio ranges. The purpose of this research was to show that in the absence of optical information on AGNs, only radio data can be used and the necessary information on the physical objects can be obtained. Regarding the example of the blazar 3C 273, the following parameters were obtained: the masses of the companions; their orbital characteristics, such as the speeds of movement in orbits; the reserves of the kinetic energy of the system; and others. It was found that AGN 3C 273 can be a very massive binary system at the stage of evolution close to merging. Based on the obtained parameters, the characteristics of the gravitational waves (GWs) of this system, its lifetime before the merger, and the possible observation of 3C 273 using gravitational wave detectors were considered.

A Close Binary Supermassive Black Hole Model for the Galaxy 3C 273

We present long-term optical multi-band photometric monitoring of the blazar OJ 287 from 6 March 2010 to 3 April 2016, with high temporal resolution in the V R I -bands. The flux variations and colour-magnitude variations on long and short timescales were investigated to understand the emission mechanisms. In our observation, the major outbursts occurred in January 2016, as predicted by the binary pair of black holes model for OJ 287, with F v a r of 1.3∼2.1%, and variability amplitude (Amp) of 5.8∼9.0%. The intra-night variability (IDV) durations were from 18.5 to 51.3 min, and the minimal variability timescale was about 4.7 min. The colour-magnitude variation showed a weak positive correlation on the long timescale with Pearson’s r = 0 . 450 , while a negative correlation was found on intra-night timescales. We briefly discuss the possible physical mechanisms that are most likely to be responsible for the observed flux and colour-magnitude correlation variability.

https://www.mdpi.com/2075-4434/5/4/85/pdf

Intra-Night Variability of OJ 287 with Long-Term Multiband Optical Monitoring

A diverse range of peculiar properties across the domains of observation have made OJ 287 one of the best-explored BL Lac objects on the issues of relativistic jets and accretion physics as well as the strong theory of gravity. We here present a brief compilation of observational results from the literature and inferences/insights from the extensive studies but focus on the interpretation of its $\sim$ 12-yr QPOOs and high energy emission mechanisms. The QPOOs in one model are attributed to the disk-impact related to dynamics of the binary SMBHs while alternative models attribute it to the geometrical effect related to the precession of a single jet or double jets. We discuss implications of the new spectral features reported during the 2015--2017 multi-wavelength high activity of the source -- a break in the NIR-optical spectrum and hardening of the MeV-GeV emission accompanied by a shift in the location of its peak, in the context of the two. The reported NIR-optical break nicely fits the description of a standard accretion disk emission from an SMBH of mass $\sim~10^{10}~M_\odot$ while the time of its first appearance in end-May 2013 (MJD 56439) is in close coincidence with the time of impact predicted by the disk-impact binary SMBH model. This spectral and temporal coincidence with the model parameters of the disk-impact binary SMBH model provides independent evidence in favor of the model over the geometrical models which argue a total central-engine mass in the range of $\rm 10^{7-9}~M_\odot$. On the other hand, the MeV-GeV spectral change is naturally reproduced by the inverse Compton scattering of photons from the broad-line region and is consistent with the detection of broad emission lines during the previous cycles of quasi-periodic outbursts. Combining this with previous SED studies suggests that in OJ 287, MeV-GeV emission results from external Comptonization.

A Multi-wavelength View of OJ 287 Activity in 2015-2017: Implications of Spectral Changes on Central-engine Models and MeV-GeV Emission Mechanism

Confirmation of the 12-year optical outburst cycle in blazar oj 287

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Confirmation of the 12-year optical outburst cycle in blazar oj 287