Search

We report the detection of a quasi-periodic oscillation (QPO) in the optical R -band light curve of the blazar S5 0716+714 spanning approximately 32 years. Using both the Weighted Wavelet Z-transform and Lomb-Scargle Periodogram methods, we identified a prominent QPO of 1060 ± 50 days at a 5 σ confidence level against the red noise background. Our findings align well with previous studies. We introduce a supermassive binary black hole (SMBBH) model to account for the observed QPO and estimate the binary system's Keplerian orbit to be 0.0053 parsec, indicating S5 0716+714 as a notable subject for upcoming nanohertz gravitational wave studies. [ABSTRACT FROM AUTHOR]

In this paper we present the RATAN-600 multi-frequency catalogue of blazars, an updated version of the BLcat: the RATAN-600 multi-frequency catalogue of BL Lacertae objects. The main novelty in the catalogue is an extension of the sample with flat-spectrum radio quasars (FSRQs), thus currently it contains more than 1700 blazars of different types. The main feature of the BLcat is a compilation of radio continuum data for blazars based on the RATAN-600 quasi-simultaneous measurements at frequencies of 1.2, 2.3, 4.7, 7.7/8.2, 11.2, and 21.7/22.3 GHz. We additionally supplement the catalogue with the radio data from external sources to provide an opportunity to more complete study of radio spectra and radio light curves. For the convenience of users, we developed tools to calculate the spectral index, variability index, and radio luminosity. We briefly describe basic radio properties of blazar subsamples of the catalogue: spectral classification, spectral indices, flux density variability, and radio luminosity. [ABSTRACT FROM AUTHOR]

We report the detection of quasi-periodic oscillations (QPOs) in the radio light curve of the blazar PKS 1510-089 spanning nearly 38 years, by means of the weighted wavelet Z-transform and Lomb–Scargle periodogram methods. Prominent QPOs with high confidence (>4 σ ) of 570 ± 30 , 800 ± 30 , and 1070 ± 40 days in the 8 GHz light curve, 430 ± 10 and 1080 ± 30 days in the 14.5 GHz light curve have been identified after estimating the significance against the red noise background. Moreover, the most significant QPO of about 1080 days exceeded 4 σ confidence level at two of the three frequencies but did not exactly persist the whole observations, indicating that QPOs in blazars are transient in nature. We suggest that the search for QPO in blazar light curves should evaluate the statistical significances and consider the influences of the colored noise, after reviewing earlier QPO claims of PKS 1510-089. [ABSTRACT FROM AUTHOR]

In this work, we compiled a sample of 1172 4FGL blazars with available spectral information and broadband intensities to the study the spectral indices. Based on this sample, we studied the correlations of spectral indices, and further studied BCU classification by using multi-band spectral indices. Among these sources, there are 196 BCUs, we manage to classify these sources into either FSRQs or BL Lacs through three methods: 1) for the α ro – α ox plane, we classified 135 sources into BL Lac candidates; 2) for the α ro – α γ plane, we classified them into 40 FSRQ candidates and 156 BL Lac candidates; and 3) for the α γ – log F plane, we classified them into 45 FSRQ candidates and 151 BL Lac candidates. From those above results, we see that 36 BCUs were consistently classified as FSRQ candidates by the latter two methods and that 128 BCUs were consistently classified as BL Lac candidates by all the three methods. The completeness is 92.9%, 88.1% and 88.1% for the corresponding result from three methods through comparing with the 4FGL updated catalogue. The correlations of spectral indices were investigated individually for FSRQs and BL Lacs. FSRQs showed very weak anti-correlations for α ro vs α γ and α ox vs α γ , positive correlation for α x γ vs α γ . On the contrary, BL Lacs showed positive correlations for α ro vs α γ and α ox vs α γ , anti-correlation for α x γ vs α γ . [ABSTRACT FROM AUTHOR]

We collect a sample of 78 Fermi detected blazars with broad line region (BLR) data and the quasi-simultaneous multi-wave band data. By analyzing the sample, we find: (1) For whole blazar sample, there exist significant correlations between radio, $\gamma$ -ray luminosity and BLR luminosity. The slope of the best-fit linear regression equation is close to the theoretical value 1. Our results provided another support of jet-disk symbiosis. (2) For FSRQ sample, we find a significant correlation between radio luminosity and optical luminosity, and weaker correlations between X-ray luminosity and radio, optical luminosity. It indicates that the X-ray band radiation mechanism is slightly different from radio and optical bands. The X-ray emission is diluted by inverse Compton scattering (IC). There is a significant correlation between BLR luminosity and $\gamma$ -ray luminosity, but no correlations between X-ray luminosity and BLR, $\gamma$ -ray luminosity, which suggests that the seed soft photons are different for IC process. From these results we suggest that the X-ray band emission is diluted by synchrotron self-Compton (SSC) process, $\gamma$ -ray band emission is produced by external Compton (EC) process. [ABSTRACT FROM AUTHOR]

Bolometric luminosity is a basic physical parameter that is widely used in the study of blazars. Due to the lack of simultaneous full wavelength data, several estimators of the bolometric luminosity are being used in practice. In this paper, we study and evaluate the reliability and significance of six estimators, the $5\mbox{GHz}$ luminosity, the 1keV luminosity, the $\gamma$ -ray luminosity, the $5\mbox{GHz}$ luminosity + the 1keV luminosity, the $5\mbox{GHz}$ luminosity + the $\gamma$ -ray luminosity and the 1keV luminosity + the $\gamma$ -ray luminosity, by analyzing the linear correlations between the integrated bolometric luminosity and them. Our main results are as follows. (i) All the six estimators are reliable in the sense that they are all significant correlated with the bolometric luminosity. (ii) Ranking from the higher significance of the reliability to lower one the six estimators are the $5\mbox{GHz}$ luminosity + the $\gamma$ -ray luminosity, the 1keV luminosity + the $\gamma$ -ray luminosity, $\gamma$ -ray luminosity, the $5\mbox{GHz}$ luminosity + the 1keV luminosity, the $5\mbox{GHz}$ luminosity and the 1keV luminosity. (iii) We suggest that the bolometric luminosity can be well estimated by the $\gamma$ -ray luminosity using the best linear equation that given in this paper for Fermi FSRQs. (iv) According to the linear regressions obtained in the analysis, we provide calibration for each estimator. [ABSTRACT FROM AUTHOR]

By means of structure function method, we have analyzed 20 blazars observed by the Rossi X-Ray Timing Explorer (RXTE) to search for possible variability period. There are the year-like periodic values in 11 of these blazars. The year-like periodicities in AO 0235+164, Mrk 501, 3C 273 and PKS 1510-089 are also found by the discrete correlation function method, the Jurkevich method and the power spectrum method. AO 0235+164, Mrk 501 and 3C 273 have possible nearly periodic values of about 370 days, 630 days and 370 days, respectively. PKS 1510-089 has two nearly periodic components, about 230 and 330 days. The year-like periodicities could be explained in the framework of a binary black hole system. The turbulence behind a shock may also give rise to the year-like periodicities, dominated by the dominant eddies' turnover times. Also, the year-like periodicities may be from the interplay of a shock with essentially helical structures wrapping around a relativistic jet. [ABSTRACT FROM AUTHOR]

In this paper, the scale invariance of the synchrotron jet of Flat Spectrum Radio Quasars has been studied using a sample of combined sources from FKM04 and from SDSS DR3 catalogue. Since the research of scale invariance has been focused on sub-Eddington cases that can be fitted onto the fundamental plane, while near-Eddington sources such as FSRQs have not been explicitly studied. The extracted physical properties of synchrotron jet of FSRQs have been shown to be scale invariant using our sample. The results are in good agreement with theoretical expectations of Heinz & Sunyaev (2003). Therefore, the jet synchrotron is shown to be scale independent, regardless of the accretion modes. Results in this article thus lend support to the scale invariant model of the jet synchrotron throughout the mass scale of black hole systems. [ABSTRACT FROM AUTHOR]

BL Lac objects are active nuclei, hosted in massive elliptical galaxies, the emission of which is dominated by a relativistic jet closely aligned with the line of sight. This implies the existence of a parent population of sources with a misaligned jet that have been identified with low-power radiogalaxies. The spectrum of BL Lacs, dominated by non-thermal emission over the whole electromagnetic range, together with bright compact radio cores, high luminosities, rapid and large amplitude flux variability at all frequencies and strong polarization makes these sources an optimal laboratory for high energy astrophysics. A most distinctive characteristic of the class is the weakness or absence of spectral lines, that historically hindered the identification of their nature and ever thereafter proved to be a hurdle in the determination of their distance. In this paper, we review the main observational facts that contribute to the present basic interpretation of this class of active galaxies. We overview the history of the BL Lac objects research field and their population as it emerged from multi-wavelength surveys. The properties of the flux variability and polarization, compared with those at radio, X-ray and gamma-ray frequencies, are summarized together with the present knowledge of the host galaxies, their environments, and central black hole masses. We focus this review on the optical observations, which played a crucial role in the early phase of BL Lacs studies, and in spite of extensive radio, X-ray, and recently gamma-ray observations, could represent the future major contribution to the unveiling of the origin of these sources. In particular, they could provide a firm conclusion on the long debated issue of the cosmic evolution of this class of active galactic nuclei and on the connection between formation of supermassive black holes and relativistic jets. [ABSTRACT FROM AUTHOR]

Light curves are usually constructed from discrete observational data by interpolation. In most cases, the observation data is temporally uneven, and therefore the light curve is usually derived by the interpolation of the binned data with the spline function, which is intended for reducing the 'high sample noise' (i.e., the variability in the timescales comparable with the bin width). Such a practice of course reduces the time resolution of the light curve. It is known that function approximation is one of the most important applications of the artificial neural networks (ANN). In this work, for the first time we tentatively use the ANN to construct light curves from unevenly sampled variability data. To demonstrate the advantages of ANN for signal reconstruction over commonly used cubic spline function scheme, two sets of simulated periodic functions are used with random noises of varying magnitudes, one single frequency based and one multiple (two) frequency based. These signal reconstruction tests show that the ANN is clearly superior to the cubic spline scheme. As a case study, we use the uneven long-term multi-band monitoring data of BL lacertae to derive the light curves with ANN. It is found that the light curves derived with ANN have higher time resolution than those with the cubic spline function adopted in previous works. We recommend using ANN for the signal reconstruction in astrophysical data analysis as well as that of in other fields. [ABSTRACT FROM AUTHOR]

We study the correlation between the emission from the broad-line region (BLR) and the emission in other wavelength ranges (from radio to x-ray) for the sample of 37 blazars (25 flat-spectrum radio quasars (FSRQs) and 10 BLLac blazars). Studying the relation between luminosities in various wavebands and the BLR luminosity is an effective method to examine the connection between the accretion rate and the luminosity of the jet.We used simultaneous RATAN-600measurements of blazar flux densities at six frequencies: 1.1, 2.3, 4.8, 7.7, 11.2, and 21.7 GHz. The observational data from other bands was taken from the literature. To determine the effect produced by the state of the object on the correlation, for the radio data we used the measurements obtained with the RATAN-600 in two states-namely, the maximum and minimum flux density values.We show that at some frequencies of the radio band, there exists a correlation of emission with the emission in the BLR for two types of blazars. In the FSRQ and BL Lac blazars, the correlation between the flux from the BLR and the flux in the radio band is indistinguishable in all cases, except for the case when a strong flux density variation was considered for the BL Lac-type of blazars (tens of percent). At the same time, the levels of significance for BL Lac (at certain frequencies p is worse than 0.05) in the active state indicate only the probable presence of connection. On the example of the sample, we show that the variability of emission significantly affects the level of correlation. Our results are consistent with the theoretical predictions about the close relationship of the accretion disk and the jet in blazars. [ABSTRACT FROM AUTHOR]

We present the Wide-field Infrared Survey Explorer (WISE) photometric data of 158 Fermi-detected BL Lacs and investigate the nature of their mid-infrared (MIR) continuum emission. In the [3.4]-[4.6]-[12] μm color-color diagram, nearly all their colors lie within the WISE Blazar strip (WBS), which is an effective diagnostic tool to separate sources dominated by non-thermal radiation from those dominated by thermal radiation. This feature indicates that their MIR emission is predominantly non-thermal. This argument is further supported by the strong radio-MIR flux correlation. We derive their MIR spectral indices and compare them with the near-infrared (NIR) spectral indices. We find that there is a prevalent steepening from MIR spectrum to NIR spectrum. The low-frequency-peaked BL Lacs (LBLs) have on average a larger MIR spectral index and a higher MIR luminosity than the high-frequency-peaked BL Lacs (HBLs), and the intermediate-frequency-peaked BL Lacs (IBLs) appear to bridge them. The MIR- γ-ray flux correlation is highly significant. A strong positive correlation is also found between the MIR and γ-ray spectral indices. The γ-ray-MIR loudness is significantly correlated with the synchrotron peak frequency. Finally we propose that the γ-rays are highly associated with the MIR emission from the jet, and the γ-ray emission is likely from the synchrotron self-Compton process for the Fermi-detected BL Lacs in our sample. [ABSTRACT FROM AUTHOR]

A wealth of information on the properties of jets in Active Galactic Nuclei (AGNs) can be derived from total flux density observations at high radio frequencies. This includes, for example, the Doppler factor, the Lorentz factor, and the viewing angle of the jet. We have earlier calculated these parameters for a sample of ∼80 sources of different AGN types using almost 20 years of 22 and 37 GHz data from Metsähovi Radio Observatory. We have now gathered data for an additional ten years, and studied the long term characteristic variability time scales of a large sample of AGNs using the first order structure function, the discrete autocorrelation function and the Lomb-Scargle periodogram. Some of the results will be presented in this paper. We also stress the importance of long term observations of AGNs, the main reason for this being misinterpretations of source properties due to insufficient time coverage. Only a few observing epochs will too easily lead to incorrect conclusions about variability, continuum spectra, and the general detectability of the source, not to mention the exclusion of interesting objects from further studies. This is particularly important when considering, for example, the Planck satellite for which the quality of the main mission product, the accurate cosmic microwave background anisotropy maps, depends heavily on the elimination of foreground sources such as AGNs. [ABSTRACT FROM AUTHOR]

We present a new population of radio quasars whose X-ray band, unlike previously known sources which have (flat) inverse Compton radiation, is characterized by (steep) synchrotron emission, with a broad-band spectral energy distribution similar to that of BL Lacs with high energy synchrotron peaks. We discuss how this new class was discovered, the class properties, and the implications of its existence for our understanding of jets and active galactic nuclei in general. [ABSTRACT FROM AUTHOR]

We compiled the radio, optical and X-ray data for SDSS sample, and presented broad band spectral index. The broad band energy distribution reveals that FSRQs and LBLs objects have similar spectral properties. However, HBLs have a separate distinct property. Even so, a unified scheme was also revealed from colour-colour diagram. [ABSTRACT FROM AUTHOR]

The nature of a substantial percentage (about one fifth) of hard X-ray sources discovered with the BAT instrument onboard the Neil Gehrels Swift Observatory (hereafter Swift) is unknown because of the lack of an identified longer-wavelength counterpart. Without such follow-up, an X-ray catalogue is of limited astrophysical value: we therefore embarked, since 2009, on a long-term project to uncover the optical properties of sources identified by Swift by using a large suite of ground-based telescopes and instruments. In this work, we continue our programme of characterization of unidentified or poorly studied hard X-ray sources by presenting the results of an optical spectroscopic campaign aimed at pinpointing and classifying the optical counterparts of 35 hard X-ray sources taken from the 70-month BAT catalogue. This sample was selected out of the available information about the chosen objects: either they are completely unidentified sources, or their association with a longer-wavelength counterpart is still ambiguous. With the use of optical spectra taken at six different telescopes we were able to identify the main spectral characteristics (continuum type, redshift, and emission or absorption lines) of the observed objects, and determined their nature. We identify and characterize a total of 41 optical candidate counterparts corresponding to 35 hard X-ray sources given that, because of positional uncertainties, multiple lower energy counterparts can sometimes be associated with higher energy detections. We discuss which ones are the actual (or at least most likely) counterparts based on our observational results. In particular, 31 sources in our sample are active galactic nuclei: 16 are classified as Type 1 (with broad and narrow emission lines) and 13 are classified as Type 2 (with narrow emission lines only); two more are BL Lac-type objects. We also identify one LINER, one starburst, and 3 elliptical galaxies. The remaining 5 objects are galactic sources: we identify 4 of them as cataclysmic variables, whereas one is a low mass X-ray binary. [ABSTRACT FROM AUTHOR]

In this paper, we compile the very-high-energy and high-energy spectral indices of 43 BL Lac objects from the literature. Based on a simple math model, ΔΓobs=αz+β, we present evidence for the origin of an observed spectral break that is denoted by the difference between the observed very-high-energy and high-energy spectral indices, ΔΓobs. We find by linear regression analysis that α≠0 and β≠0. These results suggest that the extragalactic background light attenuation and the intrinsic curvature dominate on the GeV-TeV γ-ray energy spectral break of BL Lac objects. We argue that the extragalactic background light attenuation is an exclusive explanation for the redshift evolution of the observed spectral break. [ABSTRACT FROM AUTHOR]

We report a ∼6.1 yr quasi-periodicity for the blazar S5 0716+714 using the radio light curves at 4.8, 8 and 14.5 GHz observed by the University of Michigan Radio Astronomical Observatory (UMRAO) from 1981 to 2012, by means of the Jurkevich, discrete correlation function (DCF) and power spectral analysis techniques. There are a general correlation among light curves at different frequencies and a time lag of 170±10 days between 4.8 and 14.5 GHz light curves can be confirmed. We also estimate the orbit parameters assuming a binary black hole system, and the magnetic field strength under the jet comoving frame. [ABSTRACT FROM AUTHOR]

We studied mid-infrared (MIR) variability of a large sample of blazars detected by LAT/Fermi (called Fermi-detected blazars) and those not detected by LAT/Fermi (called non-Fermi-detected blazars) in order to investigate any difference in the variability characteristics between them as well as between FSRQs and BL Lacs. Making use of NEOWISE archival data from October 2013 to December 2017, we constructed the long-term 3.4 μm and 4.6 μm light curves of 2,573 blazars and computed their intrinsic variability amplitudes, Ψ. As a result, we found that (1) Fermi-detected blazars show higher Ψ than non-Fermi-detected blazars; (2) Fermi-detected FSRQs show higher Ψ than non-Fermi-detected FSRQs; (3) Fermi-detected BL Lacs show higher Ψ than non-Fermi-detected BL Lacs; (4) FSRQs show higher Ψ than BL Lacs. By comparing their distributions of “var_flg” in the ALLWISE database, we also found that Fermi-detected blazars/FSRQs/BL Lacs tend to be more variable than non-Fermi-detected blazars/FSRQs/BL Lacs. For the Fermi-detected blazars, there are highly significant correlations between the flux densities and spectral indices in the MIR and gamma-ray bands. These results imply that the activity in the two bands is connected. Our results are consistent with several earlier results on the differences between Fermi-detected blazars and non-Fermi-detected blazars. We also give some possible explanations about the statistical results. [ABSTRACT FROM AUTHOR]

In this paper, multiwavelength chromatic luminosity at radio (logLR), optical (logLO), X-ray (logLX), and γ-rays (logLγ) for a sample of 442 Fermi blazars with known redshifts are collected from Fan et al. (2016), to study the correlations between the γ-rays and the low-energy bands using a multiple linear regression analysis. In this way, we can see which band is more important for the γ-ray emissions. Mutual correlation analysis is also used to discuss the correlations between the γ-ray and the low energy bands for the whole sample and subclasses. We come to following conclusions: The multiple linear correlation indicates that the γ-rays are correlated with the radio, optical and the X-ray emissions for the whole sample and the subclasses of flat spectrum radio quasars (FSRQs) and BL Lac objects (BL Lacs), the correlation between the γ-rays and the radio emissions is the strongest one.For BL Lacs, the optical emissions are more important than the X-rays for the γ-rays, while the X-ray emissions are more important than optical ones in FSRQs.The γ-ray emissions in HBL are from an synchrotron self-Compton, while those in FSRQs may be from external Compton and synchrotron self-Compton as well. [ABSTRACT FROM AUTHOR]