Blazars are a subclass of active galactic nuclei (AGNs) with extreme observation properties, which is caused by the beaming effect, expressed by a Doppler factor, in a relativistic jet. Doppler factor is an important parameter in the blazars paradigm to indicate all of the observation properties, and many methods were proposed to estimate its value. In this paper, we present a method following Mattox et al. to calculate the lower limit on gamma-ray Doppler factor for 809 selected Fermi/LAT-detected gamma-ray blazars by adopting the available gamma-ray and X-ray data. Our sample included 342 flat-spectrum radio quasars (FSRQs) and 467 BL Lac objects (BL Lacs), out of which 507 sources are compiled with available radio core-dominance parameter (R) from our previous study. Our calculation shows that the average values of the lower limit on gamma-ray Doppler factor for FSRQs and BL Lacs are 6.87 and 4.31, respectively. We compare and discuss our results with those from the literature. We found that the derived lower limit on gamma-ray Doppler factor for some sources are higher than that from the radio estimation, which could be possibly explained by the jet bending within those blazars. Our results also suggest that the gamma-ray and radio regions perhaps share the same relativistic effects. The gamma-ray Doppler factor has been found to be correlated with both the gamma-ray luminosity and core-dominance parameter, implying that the jet is possibly continuous in the gamma-ray bands, and R is perhaps an indicator for a beaming effect.
In this work, we compiled a sample of 202 Fermi/LAT blazars with available broad line emissions. Out of the 202 sources, 66 have known Doppler factors. The correlation between ($γ$-ray) and broad-line emission, and that between radio and broad-line emission are investigated by removing the effects of redshift and beaming boosting for the whole sample and the subclasses, flat spectrum radio quasars (FSRQs) and BL Lacertae objects (BL Lacs) respectively. We obtained a strong positive correlation between ($γ$-ray) and broad-line emission and between radio and broad-line emission for the 202 blaza…
We examine the scenario that the Doppler factor determines the observational differences of blazars in this paper. Significantly negative correlations are found between the observational synchrotron peak frequency and the Doppler factor. After correcting the Doppler boosting, the intrinsic peak frequency further has a tightly linear relation with the Doppler factor. It is more interesting that this relation is consistent with the scenario that the black hole mass governs both the bulk Lorentz factor and the synchrotron peak frequency. In addition, the distinction of the kinetic jet powers betw…
Recent population studies have shown that the variability Doppler factors can adequately describe blazars as a population. We use the flux density variations found within the extensive radio multi-wavelength datasets of the F-GAMMA program, a total of 10 frequencies from 2.64 up to 142.33 GHz, in order to estimate the variability Doppler factors for 58 $γ$-ray bright sources, for 20 of which no variability Doppler factor has been estimated before. We employ specifically designed algorithms in order to obtain a model for each flare at each frequency. We then identify each event and track its ev…
Blazar population models have shown that the inverse-Compton and variability Doppler factor estimates yield consistent results at the population level for flat spectrum radio quasars (FSRQs). The two methods, however, are inconsistent when compared on a source-by-source basis. In this work, we attempt to understand the source of the discrepancy by tracing the potential sources of systematic and statistical error for the inverse-Compton Doppler factors. By eliminating these sources of error, we provide stronger constrains on the value of the Doppler factor in blazar jets. We re-estimate the inv…
We compile 23 Gamma-ray Bursts (GRBs) and 21 blazars with estimated Doppler factors, and the Doppler factors of GRBs are estimated from their Lorentz factors by assuming their jet viewing angles θ->0 degree. Using the conventional assumption that the prompt emission of GRBs is dominated by the synchrotron radiation, we calculate the synchrotron luminosity of GRBs from their total isotropic energy and burst duration. Intriguingly, we discover a uniform correlation between the synchrotron luminosity and Doppler factor, L_syn \propto D^3.1, for GRBs and blazars, which suggests that they may share…
Relativistic effects dominate the emission of blazar jets complicating our understanding of their intrinsic properties. Although many methods have been proposed to account for them, the variability Doppler factor method has been shown to describe the blazar populations best. We use a Bayesian hierarchical code called {\it Magnetron} to model the light curves of 1029 sources observed by the Owens Valley Radio Observatory's 40-m telescope as a series of flares with an exponential rise and decay, and estimate their variability brightness temperature. Our analysis allows us to place the most strin…
Beaming effect is important for the observational properties of blazars. In this work, we collect 91 $Fermi$ blazars with available radio Doppler factors. $γ$-ray Doppler factors are estimated and compared with radio Doppler factors for some sources. The intrinsic (de-beamed) $γ$-ray flux density ($f^{\rm in}_γ$), intrinsic $γ$-ray luminosity ($L^{\rm in}_γ$), and intrinsic synchrotron peak frequency ($ν_{\rm p}^{\rm in}$) are calculated. Then we study the correlations between $f^{\rm in}_γ$ and redshift and find that they follow the theoretical relation: $\log f = -2.0 \log z + {\rm const}$. …
In a companion paper we presented a statistical model for the blazar population, consisting of distributions for the unbeamed radio luminosity function and the Lorentz factor distribution of each of the BL Lac and Flat Spectrum Radio Quasar (FSRQ) classes. Our model has been optimized so that it reproduces the MOJAVE distributions of apparent speeds and redshifts when the appropriate flux limit is applied and a uniform distribution of jet viewing angles is assumed for the population. Here we use this model to predict the Doppler factor distribution for various flux-limited samples for which Do…
Based on its broad-band spectral energy distribution, and the X-ray spectrum in particular, the radio-loud active galactic nucleus (AGN) SDSS J102623.61+254259.5 (J1026+2542) has recently been classified as a blazar. The extremely high redshift of the source, z=5.3, makes it one of the most distant and most luminous radio-loud AGN known to date. From published 5-GHz very long baseline interferometry (VLBI) imaging data obtained in 2006, the source has a typical blazar appearance on mas scales, with a prominent one-sided jet extending to ~20 mas. We estimate the brightness temperature of J1026+…
We present multi-epoch, parsec-scale core brightness temperature observations of 447 AGN jets from the MOJAVE and 2cm Survey programs at 15 GHz from 1994 to 2019. The brightness temperature of each jet over time is characterized by its median value and variability. We find that the range of median brightness temperatures for AGN jets in our sample is much larger than the variations within individual jets, consistent with Doppler boosting being the primary difference between the brightness temperatures of jets in their median state. We combine the observed median brightness temperatures with ap…
Blazars are active galactic nuclei (AGN) whose relativistic jets point nearly to the line of sight. Their compact radio structure can be imaged with very long baseline interferometry (VLBI) on parsec scales. Blazars at extremely high redshifts provide a unique insight into the AGN phenomena in the early Universe. We observed four radio sources at redshift $z>4$ with the European VLBI Network (EVN) at 1.7 and 5 GHz. These objects were previously classified as blazar candidates based on X-ray observations. One of them, J2134$-$0419 is firmly confirmed as a blazar with our VLBI observations, due …
Blazars are among the most powerful extragalactic objects, as a sub-class of active galactic nuclei. They launch relativistic jets and their emitted radiation shows strong variability across the entire electro-magnetic spectrum. The mechanisms producing the variability are still controversial and different models have been proposed to explain the observed variations in multi-frequency blazar light curves.We investigate the capabilities of the classical shock-in-jet model to explain and reconstruct the observed evolution of flares in the turnover frequency turnover flux density plane and their …
Magnetically-driven non-stationary acceleration of jets in AGNs results in the leading parts of the flow been accelerated to much higher Lorentz factors than in the case of steady state acceleration with the same parameters. The higher Doppler-boosted parts of the flow may dominate the high energy emission of blazar jets. We suggest that highly variable GeV and TeV emission in blazars is produced by the faster moving leading edges of highly magnetized non-stationary ejection blobs, while the radio data trace the slower-moving bulk flow. Model predictions compare favorably with the latest Fermi…
Blazar emission is dominated by non-thermal radiation from a relativistic jet pointing toward us, therefore undergoing Doppler beaming. This is responsible for flux enhancement and contraction of the variability time scales, so that most blazars appear as luminous sources characterized by noticeable and fast flux changes at all frequencies. The mechanisms producing their unpredictable variability are debated and include injection, acceleration and cooling of particles, with possible intervention of shock waves or turbulence. Changes in the viewing angle of the emitting knots or jet regions hav…
In the present work we propose an innovative estimation method for the minimum Doppler factor and energy content of the gamma-ray emitting region of quasar 3C 279, using a standard proton synchrotron blazar model and the principles of automatic photon quenching. The latter becomes relevant for high enough magnetic fields and results in spontaneous annihilation of gamma-rays. The absorbed energy is then redistributed into electron-positron pairs and soft radiation. We show that as quenching sets an upper value for the source rest-frame gamma-ray luminosity, one has, by neccessity, to resort to …
We use the complete MOJAVE 1.5 Jy sample of active galactic nuclei (AGN) to examine the gamma-ray detection statistics of the brightest radio-loud blazars in the northern sky. We find that 23% of these AGN were not detected above 0.1 GeV by the Fermi LAT during the 4-year 3FGL catalog period partly because of an instrumental selection effect, and partly due to their lower Doppler boosting factors. Blazars with synchrotron peaks in their spectral energy distributions located below $10^{13.4}$ Hz also tend to have high-energy peaks that lie below the 0.1 GeV threshold of the LAT, and are thus le…
Blazars are a subclass of radio-loud active galactic nuclei (AGNs), where the jet is aligned close to the line of sight. Blazars emission is dominated by non-thermal processes, where Doppler boosted radiation originates from a relativistic population of charged particles within the jet. From radio to TeV energies, blazars are highly variable on timescales from minutes to several months. There are several mechanisms proposed to explain variability, including changes in the viewing angle of the jet, propagating along the rotation axis of the accretion disc. The misalignment of a supermassive bla…
Based on a large Fermi blazar sample, the blazar sequence (synchrotron peak frequency $ν_{\rm peak}$ versus synchrotron peak luminosity $L_{\rm peak}$) is revisited. It is found that there is significant anti-correlation between $ν_{\rm peak}$ and $L_{\rm peak}$ for blazars. However, after being Doppler corrected, the anti-correlation disappears. The jet cavity power ($P_{\rm jet}$) is estimated from extended radio luminosity. So it is free of beaming effect. We find that there are significant anti-correlations between $P_{\rm jet}$ and beam-corrected $ν_{\rm peak}^{'}$ for both blazars and ra…
Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the time scale of their radio flares. In this $Letter$, we use multiwavelength data and Doppler factors reported in the literatures for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distribution…
I show that by assuming a standard Blandford-Konigl jet, it is possible to determine the bulk Lorentz factor and angle to the line of sight of self-similar parsec-scale blazar jets by using five measured quantities: redshift, core radio flux, extended radio flux, the magnitude of the core shift between two frequencies, and apparent jet opening angle. From the bulk Lorentz factor and angle computed with this method, one can compute other jet properties such as the Doppler factor, magnetic field strength, and intrinsic jet opening angle. I use data taken from the literature and marginalize over …
Active galactic nuclei are the most luminous persistent (non-transient, even if often variable) objects in the Universe. They are bright in the entire electromagnetic spectrum. Blazars are a special class where the jets point nearly to our line of sight. Because of this special geometry and the bulk relativistic motion of the plasma in the jet, their radiation is enhanced by relativistic beaming. The majority of extragalactic objects detected in gamma-rays are blazars. However, finding their counterparts in other wavebands could be challenging. Here we present the results of our 5-GHz European…
Black holes, anywhere in the stellar-mass to supermassive range, are often associated with relativistic jets. Models suggest that jet production may be a universal process common in all black hole systems regardless of their mass. Although in many cases observations support such hypotheses for microquasars and Seyfert galaxies, little is known on whether boosted blazar jets also comply with such universal scaling laws. We use uniquely rich multiwavelength radio light curves from the F-GAMMA program and the most accurate Doppler factors available to date to probe blazar jets in their emission r…
Previous spectral energy distribution modeling based on XMM-Newton X-ray observation of the classical double-lobed radio galaxy 3C 411 left the possibility open for the presence of a blazar-like core. We investigated this scenario by characterizing the radio brightness distribution in the inner ~10-pc region of the source. We applied the very long baseline interferometry (VLBI) technique at four different frequencies from 1.7 to 7.6 GHz. We analyzed archival data from the Very Long Baseline Array (VLBA) taken in 2014, and data from the European VLBI Network (EVN) obtained in 2017. The VLBI ima…
We investigate the dependence of gamma-ray brightness of blazars on intrinsic properties of their parsec-scale radio jets and the implication for relativistic beaming. By combining apparent jet speeds derived from high-resolution VLBA images from the MOJAVE program with millimetre-wavelength flux density monitoring data from Metsahovi Radio Observatory, we estimate the jet Doppler factors, Lorentz factors, and viewing angles for a sample of 62 blazars. We study the trends in these quantities between the sources which were detected in gamma-rays by the Fermi Large Area Telescope (LAT) during it…
We use the third catalog of blazars detected by Fermi/LAT (3LAC) and gamma-ray Narrow-line Seyfert 1 Galaxies (gamma-NLSy1s) to study the blazar sequence and relationship between them. Our results are as follows: (i) There is a weak anti-correlation between synchrotron peak frequency and peak luminosity for both Fermi blazars and gamma-NLSy1s, which supports the blazar sequence. However, after Doppler correction, the inverse correlation disappeared, which suggests that anti-correlation between synchrotron peak frequency and peak luminosity is affected by the beaming effect. (ii) There is a sig…
CAZ catalog and optical light curves of 7918 blazar-selected active galactic nuclei
University of Turku（图尔库大学）；Finnish Centre for Astronomy with ESO (FINCA)（芬兰ESO天文中心）；Aalto University（阿尔托大学）；Aalto University Metsähovi Radio Observatory（阿尔托大学梅塔霍维射电天文台）；Aalto University Department of Electronics and Nanoengineering（阿尔托大学电子与纳米工程系）；Institute of Astrophysics, Foundation for Research and Technology-Hellas（希腊研究与技术基金会天体物理研究所）；Norwegian University of Science and Technology（挪威科技大学）
High-energy astrophysical neutrinos have been observed by several telescopes in the last decade, but their sources still remained unknown. We address the problem of locating astrophysical neutrinos' sources in a statistical manner. We show that blazars positionally associated with IceCube neutrino detections have stronger parsec-scale radio cores than the rest of the sample. The probability of a chance coincidence is only 4*10^-5 corresponding to a significance of 4.1 sigma. We explicitly list four strong radio blazars as highly probable sources of neutrinos above 200 TeV: 3C 279, NRAO 530, PK…
Variability in active galactic nuclei is observed in ultraviolet to X-ray emission based light curves. This could be attributed to orbital signatures of the plasma that constitutes the accretion flow on the putative disk or in the developing jet close to the inner region of the central black hole. We discuss some theoretical models which build on this view. These models include general relativistic effects such as light bending, aberration effects, gravitational and Doppler redshifts. The novel aspects relate to the treatment of helical flow in cylindrical and conical geometries in the vicinit…
Quasi-Simultaneous Broadband Spectral Energy Distributions of a Sample of Fermi Blazars -- I. Correlation Results
Zhejiang Normal University（浙江师范大学）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；University of Science and Technology of China（中国科学技术大学）；Shanghai Normal University（上海师范大学）；Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；Center for Astronomical Mega-Science, Chinese Academy of Sciences（中国科学院国家天文台）；College of Physics and Electronic Engineering, Qilu Normal University（齐鲁师范学院物理与电子工程学院）
School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（教育部现代天文学和天体物理学重点实验室（南京大学））；Centre for Space Research, North-West University（西北大学空间研究中心）
We have recently proposed a new scenario where blazars are classified as flat-spectrum radio quasars or BL Lacs according to the prescriptions of unified schemes, and to a varying combination of Doppler boosted radiation from the jet, emission from the accretion disk, the broad line region, and light from the host galaxy. This mix of different components leads to strong selection effects, which are properly taken into account in our scheme. We describe here the main features of our approach, which solves many long-standing issues of blazar research, give the most important results, and discuss…
The origin of gamma-ray flares observed from blazars is one of the major mysteries in jet physics. We have attempted to address this problem following a novel spectral energy distribution (SED) fitting technique that explored the flaring patterns identified in the broadband SEDs of two gamma-ray bright blazars 3C 279 (z=0.54) and 3C 454.3 (z=0.86), using near-simultaneous radio-to-gamma-ray observations. For both sources, the gamma-ray flux strongly correlates with the separation of the SED peaks and the Compton dominance. We propose that spectral hardening of the radiating electron population…
We analyze the parsec-scale jet kinematics from 2007 June to 2018 December of a sample of $γ$-ray bright blazars monitored roughly monthly with the Very Long Baseline Array at 43 GHz under the VLBA-BU-BLAZAR program. We implement a novel piece-wise linear fitting method to derive the kinematics of 521 distinct emission knots from a total of 3705 total intensity images in 22 quasars, 13 BL Lacertae objects, and 3 radio galaxies. Apparent speeds of these components range from $0.01c$ to $78c$, and 18.6\% of knots (other than the "core") are quasi-stationary. One-fifth of moving knots exhibit non…
We report on X-ray measurements constraining the spectral energy distribution (SED) of the high-redshift $z=5.18$ blazar SDSS J013127.34$-$032100.1 with new XMM-Newton and NuSTAR exposures. The blazar's X-ray spectrum is well fit by a power law with $Γ=1.9$ and $N_{\rm H}=1.1\times10^{21}\rm \ cm^{-2}$, or a broken power law with $Γ_l=0.5$, $Γ_h=1.8$, and a break energy $E_b=0.7$ keV for an expected absorbing column density of $N_{\rm H}=3.6\times 10^{20}\rm \ cm^{-2}$, supported by spectral fitting of a nearby bright source. No additional spectral break is found at higher X-ray energies (1-30…
Aiming to delineate the physical framework of blazars, we present an effective method to estimate four important parameters based on the idea proposed by \citet{BK95}, including the upper limit of central black hole mass $M$, the Doppler factor $δ$, the distance along the axis to the site of the $γ$-ray production $d$ (which then can be transformed into the location of $γ$-ray-emitting region $R_γ$) and the propagation angle with respect to the axis of the accretion disk $Φ$. To do so, we adopt an identical sample with 809 {\it Fermi}-LAT-detected blazars which had been compiled in \citet{Pei2…
PG 1553+113 is the first blazar showing an approximately two-year quasi-periodic pattern in its gamma-ray light curve. Such quasi-periodicity might have a geometrical origin, possibly related to the precessing nature of the jet, or could be intrinsic to the source and related to pulsational accretion flow instabilities. By means of a ~2yr very long baseline array (VLBA) monitoring at 15, 24, and 43 GHz we investigate the source pc-scale properties during an entire cycle of gamma-ray activity in the period 2015-2017. In contrast to the well-defined periodicity in the gamma-ray emission, at radi…
The radio quasar NVSS J141922$-$083830 (J1419$-$0838) was initially classified as an uncategorised blazar-type object, following its detection in the $γ$-ray band with the Fermi space telescope. Later, using multi-waveband observations and modeling, its was found to be a flat-spectrum radio quasar (FSRQ). However, its radio emission has never been discussed in depth in the literature. Here we present a detailed analysis on the radio properties of J1419$-$0838 using archival interferometric imaging data at pc and kpc scales. We conclude that the flux density variations, the flat radio spectrum,…
In a two-component jet model, the emissions are the sum of the core and extended emissions: $S^{\rm ob}=S_{\rm core}^{\rm ob}+S_{\rm ext}^{\rm ob}$, with the core emissions, $S_{\rm core}^{\rm ob}= f S_{\rm ext}^{\rm ob}δ^{q}$, being a function of the Doppler factor, $δ$, the extended emission, $S_{\rm ext}^{\rm ob}$, jet type dependent factor, $q$, and the ratio of the core to the extended emissions in the comoving frame, $f$. The $f$ is an unobservable but important parameter. Following our previous work, we collect 65 blazars with available Doppler factor, $δ$, superluminal velocity, $β_{ap…
Radio-loud sources with blazar-like properties, but having a jet that does not directly point in the direction of the observer are among the most interesting classes of gamma-ray emitters. These sources are known as Misaligned Active Galactic Nuclei (MAGN). Understanding MAGN properties is useful to improve the knowledge of blazar energetics. We searched for new MAGN candidates among the remaining blazars of uncertain type detected by the Fermi Large Area Telescope (LAT) using a methodology based on characterizing their radio morphology. We identified seven new candidates associated with gamma…
Blazars show rapid and violent variabilities, which timescale are often less than a day. We studied intraday variations by applying a shot analysis technique to Kepler monitoring of blazar W2R 1926+42 in Quarter 14. We obtained a mean profile calculated from 195 rapid variations. The mean profile shows three components; one is a sharp structure distributed within $\pm$0.1 day of the peak, and two slow-varying components. This spiky-peak component reflects features of rapid variations directly. The profile of peak component shows an exponential rise and decay of which timescales are different, …
Blazar radiation is dominated by a relativistic jet which can be modeled at first approximation using just two intrinsic parameters - the Lorentz factor $Γ$ and the viewing angle $θ$. Blazar jet observations are often beamed due to relativistic effects, complicating the understanding of these intrinsic properties. The most common way to estimate blazar Lorentz factors needs the estimation of apparent jet speeds and Doppler beaming factors. We present a new and independent method of constructing the blazar Lorentz factor distribution, using the optical fundamental plane of black hole activity. …
The quasar 3C454.3 underwent a uniquely-structured multi-frequency outburst in June 2016. The blazar was observed in the optical $R$ band by several ground-based telescopes in photometric and polarimetric modes, at $γ$-ray frequencies by the \emph{Fermi}\ Large Area Telescope, and at 43 GHz with the Very Long Baseline Array. The maximum flux density was observed on 2016 June 24 at both optical and $γ$-ray frequencies, reaching $S^\mathrm{max}_\mathrm{opt}=18.91\pm0.08$ mJy and $S_γ^\mathrm{max} =22.20\pm0.18\times10^{-6}$ ph cm$^{-2}$ s$^{-1}$, respectively. The June 2016 outburst possessed a …
We analyze the parsec-scale jet kinematics from 2007 June to 2013 January of a sample of $γ$-ray bright blazars monitored roughly monthly with the Very Long Baseline Array at 43~GHz. In a total of 1929 images, we measure apparent speeds of 252 emission knots in 21 quasars, 12 BL~Lacertae objects (BLLacs), and 3 radio galaxies, ranging from 0.02$c$ to 78$c$; 21\% of the knots are quasi-stationary. Approximately 1/3 of the moving knots execute non-ballistic motions, with the quasars exhibiting acceleration along the jet within 5~pc (projected) of the core, and knots in the BLLacs tending to dece…
We present RadioAstron Space VLBI imaging observations of the BL Lac object S5 0716+71 made on January 3-4 2015 at a frequency of 22 GHz (wavelength $λ=1.3$ cm). The observations were made in the framework of the AGN Polarization Key Science Program. The source was detected on projected space-ground baselines up to 70 833 km (5.6 Earth diameters) for both, parallel hand and cross-hand interferometric visibilities. We have used these detections to obtain a full-polarimetric image of the blazar at an unprecedented angular resolution of 24 $μ$as, the highest for this source to date. This enabled …
Utilizing all the 16-year $RXTE$ observations, we analyze the X-ray spectra of 32 TeV blazars, and perform a systematic investigation of X-ray spectral variability for the 5 brightest sources during their major flares that lasted several days. We obtain photon spectral index ($α$), flux and synchrotron radiation peak energy ($E_{\rm{p}}$) from empirical spectral fitting, and electron spectral index ($p$) from theoretical synchrotron radiation modeling. We find that both $α$ and $p$ generally display a harder-when-brighter trend, confirming the results of many previous works. Furthermore, we co…
Jet origination is one of the most important questions of AGN, yet it stays obscure. In this work, we made use of information of emission lines, spectral energy distributions (SEDs), \textit{Fermi}-LAT $γ$-ray emission, construct a blazar sample that contains 667 sources. We notice that jet power originations are different for BL Lacs and for FSRQs. The correlation between jet power $P_{\rm jet}$ and the normalized disk luminosity $L_{\rm Disk}/L_{\rm Edd}$ shows a slope of -1.77 for BL Lacs and a slope of 1.16 for FSRQs. The results seem to suggest that BL Lac jets are powered by extracting b…
Active galactic nuclei come in many varieties. A minority of them are radio-loud, and exhibit two opposite prominent plasma jets extending from the proximity of the supermassive black hole up to megaparsec distances. When one of the relativistic jets is oriented closely to the line of sight, its emission is Doppler beamed and these objects show extreme variability properties at all wavelengths. These are called "blazars". The unpredictable blazar variability, occurring on a continuous range of time-scales, from minutes to years, is most effectively investigated in a multi-wavelength context. G…
The intergalactic magnetic field (IGMF) in cosmic voids can be indirectly probed through its effect on electromagnetic cascades initiated by a source of TeV gamma rays, such as blazars, a subclass of active galactic nuclei. Blazars that are sufficiently luminous at TeV energies, "extreme TeV blazars", can produce detectable levels of secondary radiation from inverse Compton scattering of the electrons in the cascade, provided that the IGMF is not too large. We reveiw recent work in the literature which utilizes this idea to derive constraints on the IGMF for three TeV-detected blazars-1ES 0229…
The mechanism for producing gamma-ray quasi-periodic oscillation (QPO) in blazar is unknown. One possibility is the geometric model, in which without the need for intrinsic quasi-periodic variation, the relativistic Doppler factor changes periodically, resulting in observed gamma-ray QPO. We propose a method to test this geometric model. We analyze the {\it Fermi}-LAT data of PG 1553+113 spanning from 2008 August until 2018 February. According to 29 four-month average spectral energy distributions (SEDs) in the energy range of 0.1-300 GeV, we split the {\it Fermi}-LAT energy range into three b…
High-redshift blazars are one of the most powerful monsters in the universe and $γ$-ray variability carries crucial information of their relativistic jets. In this work we present results of the first systematical temporal analysis of {\it Fermi}-LAT data of all known seven $γ$-ray blazars beyond redshift 3. Significant long-term $γ$-ray variability is found from five sources in monthly $γ$-ray light curves, in which three of them are reported for the first time. Furthermore, intraday $γ$-ray variations are detected from NVSS J053954$-$283956 and NVSS J080518$+$614423. Doubling variability tim…
The γ-ray loud blazars (flat spectrum radio quasars--FSRQs and BL Lacertae objects-BLs) are very bright in the γ-ray bands, which is perhaps associated with a beaming effect. Therefore, one can expect that the γ-ray luminosity is correlated with the beaming factor. In this paper, we investigated the relation between the radio Doppler factors and the gamma-ray luminosities. Our analysis suggests that the γ-ray luminosity be strongly correlated with the factor of δ_R for the whole sample, FSRQs, and BLs. When the effect of a common redshift is excluded, the correlation still exists for the FSRQs…
The observations of TeV blazars published recently show an unexpected quadratic or even cubic correlation between the X-ray and gamma-ray emission. A standard model of the synchrotron self-Compton emission of a compact source inside a jet is not able to explain such a correlation. Therefore, we propose an alternative scenario where the emission of at least two independent compact components is observed at the same time. We compare two different models. The first model assumes the injection of relativistic particles into a downstream region of a shock wave inside a jet that creates the emitting…
