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Aims. In the framework of the multi-wavelength and very long baseline interferometry (VLBI) monitoring program TANAMI (Tracking Active Nuclei with Austral Milliarcsecond Interferometry), we study the evolution of the parsec-scale radio emission in radio galaxies in the southern hemisphere and their relationship to the γ-ray properties of the sources. Our study investigates systematically, for the first time, the relationship between the two energy regimes in radio galaxies. In this first paper, we focus on Fermi-LAT-detected sources. Methods. The TANAMI program monitors a large sample of radio-loud AGN at 8.4 GHz and 22.3 GHz with the Australian long baseline array (LBA) and associated telescopes in Antarctica, Chile, New Zealand and South Africa. We performed a kinematic analysis for five γ-ray detected radio galaxies using multi-epoch 8.4 GHz VLBI images, deriving limits on intrinsic jet parameters such as speed and viewing angle. We analyzed 103 months of Fermi-LAT data in order to study possible connections between the γ-ray properties and the pc-scale jets of Fermi-LAT-detected radio galaxies, both in terms of variability and average properties. We discuss the individual source results and draw preliminary conclusions on sample properties including published VLBI results from the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) survey, with a total of fifteen sources. Results. We find that the first γ-ray detection of Pictor A might be associated with the passage of a new VLBI component through the radio core, which appears to be a defining feature of high-energy emitting Fanaroff-Riley type II radio galaxies. We detect subluminal parsec-scale jet motions in the peculiar AGN PKS 0521−36, and we confirm the presence of fast γ-ray variability in the source down to timescales of six hours, which is not accompanied by variations in the VLBI jet. We robustly confirm the presence of significant superluminal motion, up to βapp ∼ 3, in the jet of the TeV radio galaxy PKS 0625−35. Our VLBI results constrain the jet viewing angle to be θ <  53°, allowing for the possibility of a closely aligned jet. Finally, by analyzing the first pc-scale multi-epoch images of the prototypical compact symmetric object (CSO) PKS 1718−649, we place an upper limit on the separation speed between the two mini-lobes. This in turn allows us to derive a lower limit on the age of the source. Conclusions. We can draw some preliminary conclusions on the relationship between pc-scale jets and γ-ray emission in radio galaxies, based on Fermi-LAT-detected sources with available multi-epoch VLBI measurements. We find that the VLBI core flux density correlates with the γ-ray flux, as seen in blazars. On the other hand, the γ-ray luminosity does not show any dependence on the core brightness temperature and core dominance, which are two common indicators of jet Doppler boosting. This seems to indicate that γ-ray emission in radio galaxies is not driven by orientation-dependent effects, as in blazars, in accordance with the unified model of jetted AGN. [ABSTRACT FROM AUTHOR]

Context. The temporal and spatial spectral evolution of the jets of active galactic nuclei (AGN) can be studied with multi-frequency, multi-epoch very-long-baseline-interferometry (VLBI) observations. The combination of both morphological (kinematical) and spectral parameters can be used to derive source-intrinsic physical properties, such as the magnetic field and the nonthermal particle density. Such a study is of special interest during the high states of activity in AGNs, since VLBI observations can provide estimates of the location of the flaring site. Furthermore, we can trace the temporal variations in the source-intrinsic parameters during the flare, which may reflect the interaction between the underlying plasma and a traveling shock wave. The source CTA102 exhibited such a radio flare around 2006. Aims. In the first two papers of this series (Papers I and II), we analyzed the single-dish light curves and the VLBI kinematics of the blazar CTA102 and suggested a shock-shock interaction between a traveling and a standing shock wave as a possible scenario to explain the observed evolution of the component associated to the 2006 flare. In this paper we investigate the core shift and spectral evolution to test our hypothesis of a shock-shock interaction. Methods. We used eight multi-frequency Very Long Baseline Array (VLBA) observations to analyze the temporal and spatial evolution of the spectral parameters during the flare. We observed CTA102 between May 2005 and April 2007 using the VLBA at six different frequencies spanning from 2 GHz up to 86GHz. After the calibrated VLBA images were corrected for opacity, we performed a detailed spectral analysis.We developed methods for aligning the images and extracting the uncertainties in the spectral parameters. From the derived values we estimated the magnetic field and the density of the relativistic particles and combined those values with the kinematical changes provided from the long-term VLBA monitoring (Paper II) and single-dish measurements (Paper I). Results. The detailed analysis of the opacity shift reveals that the position of the jet core is proportional to ʋ-1 with some temporal variations. The value suggests possible equipartition between magnetic field energy and particle kinetic energy densities at the most compact regions. From the variation in the physical parameters we deduced that the 2006 flare in CTA102 is connected to the ejection of a new traveling feature (tej = 2005.9) and to the interaction between this shock wave and a stationary structure (interpreted as a recollimation shock) around 0.1 mas from the core (de-projected 18 pc at a viewing angle of φ = 2.6°). The source kinematics, together with the spectral and structural variations, can be described by helical motions in an overpressured jet. [ABSTRACT FROM AUTHOR]

Context. Very Long Baseline Interferometry (VLBI) observations can resolve the radio structure of active galactic nuclei (AGN) and provide estimates of the structural and kinematic characteristics on parsec-scales in their jets. The changes in the kinematics of the observed jet features can be used to study the physical conditions in the innermost regions of these sources. We performed multifrequency multiepoch Very Long Baseline Array (VLBA) observations of the blazar CTA102 during its 2006 radio flare, the strongest ever reported for this source. These observations provide an excellent opportunity to investigate the evolution of the physical properties of blazars, especially during these flaring events Aims. We want to study the kinematic changes in the source during the strong radio outburst in April 2006 and test the assumption of a shock-shock interaction. This assumption is based on the analysis and modeling of the single-dish observations of CTA102 (Paper I). Methods. In this paper we study the kinematics of CTA102 at several frequencies using VLBI observations. From the modeled jet features we derived estimates for the evolution of the physical parameters, such as the particle density and the magnetic field. Furthermore, we combined our observations during the 2006 flare with long-term VLBA monitoring of the source at 15GHz and 43 GHz. Results. We cross-identified seven features throughout our entire multifrequency observations and find evidence of two possible recollimation shocks around 0.1mas (deprojected 18 pc at a viewing angle ϑ = 2.6°) and 6.0mas (deprojected 1 kpc) from the core. The 43 GHz observations reveal a feature ejected at epoch tej = 2005.9 ± 0.2, which could be connected to the 2006 April radio flare. Furthermore, this feature might be associated with the traveling component involved in the possible shock-shock interaction, which gives rise to the observed double peak structure in the single-dish light curves reported in Paper I. [ABSTRACT FROM AUTHOR]

Context. 3C 84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of very-long-baseline interferometry (VLBI) above the hitherto available maximum frequency of 86 GHz. Aims. Using ultrahigh resolution VLBI observations at the currently highest available frequency of 228 GHz, we aim to perform a direct detection of compact structures and understand the physical conditions in the compact region of 3C 84. Methods. We used Event Horizon Telescope (EHT) 228 GHz observations and, given the limited (u, v)-coverage, applied geometric model fitting to the data. Furthermore, we employed quasi-simultaneously observed, ancillary multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure. Results. We report the detection of a highly ordered, strong magnetic field around the central, supermassive black hole of 3C 84. The brightness temperature analysis suggests that the system is in equipartition. We also determined a turnover frequency of νm = (113 ± 4) GHz, a corresponding synchrotron self-absorbed magnetic field of BSSA = (2.9 ± 1.6) G, and an equipartition magnetic field of Beq = (5.2 ± 0.6) G. Three components are resolved with the highest fractional polarisation detected for this object (mnet = (17.0 ± 3.9)%). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017–2018. We report a steeply negative slope of the spectrum at 228 GHz. We used these findings to test existing models of jet formation, propagation, and Faraday rotation in 3C 84. Conclusions. The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C 84. However, systematic uncertainties due to the limited (u, v)-coverage, however, cannot be ignored. Our upcoming work using new EHT data, which offer full imaging capabilities, will shed more light on the compact region of 3C 84. [ABSTRACT FROM AUTHOR]

Context. Supermassive black holes in the centres of radio-loud active galactic nuclei (AGN) can produce collimated relativistic outflows (jets). Magnetic fields are thought to play a key role in the formation and collimation of these jets, but the details are much debated. Aims. We study the innermost jet morphology and magnetic field strength in the AGN 3C 345 with an unprecedented resolution using images obtained within the framework of the key science programme on AGN polarisation of the Space VLBI mission RadioAstron. Methods. We observed the flat spectrum radio quasar 3C 345 at 1.6 GHz on 2016 March 30 with RadioAstron and 18 ground-based radio telescopes in full polarisation mode. Results. Our images, in both total intensity and linear polarisation, reveal a complex jet structure at 300 μas angular resolution, corresponding to a projected linear scale of about 2 pc or a few thousand gravitational radii. We identify the synchrotron self-absorbed core at the jet base and find the brightest feature in the jet 1.5 mas downstream of the core. Several polarised components appear in the Space VLBI images that cannot be seen from ground array-only images. Except for the core, the electric vector position angles follow the local jet direction, suggesting a magnetic field perpendicular to the jet. This indicates the presence of plane perpendicular shocks in these regions. Additionally, we infer a minimum brightness temperature at the largest (u, v)-distances of 1.1 × 1012 K in the source frame, which is above the inverse Compton limit and an order of magnitude larger than the equipartition value. This indicates locally efficient injection or re-acceleration of particles in the jet to counter the inverse Compton cooling or the geometry of the jet creates significant changes in the Doppler factor, which has to be > 11 to explain the high brightness temperatures. [ABSTRACT FROM AUTHOR]

Context. Flares in radio-loud active galactic nuclei are thought to be associated with the injection of fresh plasma into the compact jet base. Such flares are usually strongest and appear earlier at shorter radio wavelengths. Hence, very long baseline interferometry (VLBI) at millimeter(mm)-wavelengths is the best-suited technique for studying the earliest structural changes of compact jets associated with emission flares. Aims. We study the morphological changes of the parsec-scale jet in the nearby (z = 0.049) γ-ray bright radio galaxy 3C 111 following a flare that developed into a major radio outburst in 2007. Methods. We analyse three successive observations of 3C 111 at 86 GHz with the Global mm-VLBI Array (GMVA) between 2007 and 2008 which yield a very high angular resolution of ∼45 μas. In addition, we make use of single-dish radio flux density measurements from the F-GAMMA and POLAMI programmes, archival single-dish and VLBI data. Results. We resolve the flare into multiple plasma components with a distinct morphology resembling a bend in an otherwise remarkably straight jet. The flare-associated features move with apparent velocities of ∼4.0c to ∼4.5c and can be traced also at lower frequencies in later epochs. Near the base of the jet, we find two bright features with high brightness temperatures up to ∼1011 K, which we associate with the core and a stationary feature in the jet. Conclusions. The flare led to multiple new jet components indicative of a dynamic modulation during the ejection. We interpret the bend-like feature as a direct result of the outburst which makes it possible to trace the transverse structure of the jet. In this scenario, the components follow different paths in the jet stream consistent with expectations for a spine-sheath structure, which is not seen during intermediate levels of activity. The possibility of coordinated multiwavelength observations during a future bright radio flare in 3C 111 makes this source an excellent target for probing the radio-γ-ray connection. [ABSTRACT FROM AUTHOR]

Context. PSO J334.2028+1.4075 (PSO J334) is a luminous quasar located at redshift z = 2.06. The source gained attention when periodic flux density variations were discovered in its optical light curve. These variations were initially interpreted as the variability due to the orbital motion of a supermassive black hole binary (SMBHB) residing in a single circumbinary accretion disk. The orbital separation was determined to be 0.006 pc with an in-spiral time of 7 yr in the rest frame of PSO J334. These findings suggested the quasar could be in the gravitational wave emitting phase of its merger and so extended multiwavelength observations were commenced. However, subsequent observations provided evidence against the binary hypothesis as no optical periodicity was found on extended time baselines. On the other hand, detailed radio analysis with the Karl G. Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA) revealed a lobe-dominated quasar at kiloparsec scales, and possibly a precessing jet, which could retain PSO J334 as a binary SMBH candidate. Aims. We aim to study both the large- and small-scale radio structures in PSO J334 to provide additional evidence for or against the binary scenario. Methods. We observed the source at 1.7 GHz with the European Very Long Baseline Interferometry Network (EVN), and at 1.5 and 6.2 GHz with the VLA, at frequencies that complement the previous radio interferometric study. Results. Our images reveal a single component at parsec scales slightly resolved in the southeast-northwest direction and a lobe-dominated quasar at kiloparsec scales with a complex structure. The source morphology and polarization in our VLA maps suggest that the jet is interacting with dense clumps of the ambient medium. While we also observe a misalignment between the inner jet and the outer lobes, we suggest that this is due to the restarted nature of the radio jet activity and the possible presence of a warped accretion disk rather than due to the perturbing effects of a companion SMBH. Conclusions. Our analysis suggests that PSO J334 is most likely a jetted active galactic nucleus with a single SMBH, and there is no clear evidence of a binary SMBH system in its central engine. [ABSTRACT FROM AUTHOR]

Context. The radio galaxy IC 310 in the Perseus cluster has recently been detected in the gamma-ray regime at GeV and TeV energies. The TeV emission shows time variability and an extraordinarily hard spectrum, even harder than the spectrum of the similar nearby gamma-ray emitting radio galaxy M87. Aims. High-resolution studies of the radio morphology help to constrain the geometry of the jet on sub-pc scales and to find out where the high-energy emission might come from. Methods. We analyzed May 2011 VLBA data of IC310 at a wavelength of 3.6 cm, revealing the parsec-scale radio structure of this source. We compared our findings with more information available from contemporary single-dish flux density measurements with the 100-m Effelsberg radio telescope. Results. We have detected a one-sided core-jet structure with blazar-like, beamed radio emission oriented along the same position angle as the kiloparsec scale radio structure observed in the past by connected interferometers. Doppler-boosting favoritism is consistent with an angle of θ ≲ 38° between the jet axis and the line-of-sight, i.e., very likely within the boundary dividing low-luminosity radio galaxies and BL Lac objects in unified schemes. Conclusions. The stability of the jet orientation from parsec to kiloparsec scales in IC 310 argues against its classification as a headtail radio galaxy; i.e., there is no indication of an interaction with the intracluster medium that would determine the direction of the tail. IC310 seems to represent a low-luminosity FRI radio galaxy at a borderline angle to reveal its BL Lac-type central engine. [ABSTRACT FROM AUTHOR]

Context. High-resolution very long baseline interferometry (VLBI) observations of NGC 1052 show a two sided jet with several regions of enhanced emission and a clear emission gap between the two jets. This gap shrinks with increasing frequency and vanishes around ν ∼ 43 GHz. The observed structures are due to both the macroscopic fluid dynamics interacting with the surrounding ambient medium including an obscuring torus and the radiation microphysics. In order to model the observations of NGC 1052 via state-of-the art numerical simulations both the fluid-dynamical and emission processes have to be taken into account. Aims. In this paper we investigate the possible physical conditions in relativistic jets of NGC 1052 by directly modelling the observed emission and spectra via state-of-the-art special-relativistic hydrodynamic (SRHD) simulations and radiative transfer calculations. Methods. We performed SRHD simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code Ratpenat. To investigate the physical conditions in the relativistic jet we coupled our radiative transfer code to evolutionary algorithms and performed simultaneous modelling of the observed jet structure and the broadband radio spectrum. During the calculation of the radiation we consider non-thermal emission from the jet and thermal absorption in the obscuring torus. In order to compare our model to VLBI observations we take into account the sparse sampling of the u-v plane, the array properties and the imaging algorithm. Results. We present for the first time an end-to-end pipeline for fitting numerical simulations to VLBI observations of relativistic jets taking into account the macro-physics including fluid dynamics and ambient medium configurations together with thermal and non-thermal emission and the properties of the observing array. The detailed analysis of our simulations shows that the structure and properties of the observed relativistic jets in NGC 1052 can be reconstructed by a slightly over-pressured jet (dk ∼ 1.5) embedded in a decreasing pressure ambient medium [ABSTRACT FROM AUTHOR]

Context. Few active galactic nuclei (AGN) reveal double-sided jet systems. However, these systems are crucial to understand basic physical properties of extragalactic jets. Aims. We address the questions whether jets in AGN are symmetric in nature, how well they are collimated on small scales, and how they evolve with time. Methods. We monitored the sub-parsec scale morphology of NGC 1052 with the Very Long Baseline Array at 43 GHz from 2005 to 2009. Results. A detailed study of 29 epochs show a remarkable asymmetry between both jets. A kinematic analysis of the outflows reveals higher apparent velocities for the eastern (approaching) jet as compared to the western (receding) jet, i.e., βej = 0.529 ± 0.038 and βwj = 0.343 ± 0.037, respectively. Contradictory to previous studies, we find higher flux densities for the western jet as compared to the eastern. The distribution of brightness temperature and jet width features well-collimated jets up to 1 mas distance to the dynamic center and a nearly conical outflow further outward. By combining flux density ratios and velocities of the jet flows, we were unable to find a combination of intrinsic velocities and inclination angles of the jets that is consistent for all four years of observation; this contradicts findings for symmetrically evolving jets. Spectral index maps between quasi-simultaneous 22 GHz and 43 GHz observations support the existence of an optically thick absorber covering the innermost ≃1.6 mas around the 43 GHz central feature and an optically thin jet emission with a spectral index of ≤−1. Conclusions. Our results fit into a picture in which we expect larger internal energy and/or magnetic flux in the western jet and higher kinetic energy in the eastern jet. Previous observations at lower frequencies have found slower velocities of the moving jet features as compared to this work. Considering the different velocities in different areas, we suggest a spine-sheath structure with a faster inner layer and slower outer layer. [ABSTRACT FROM AUTHOR]

Context. High resolution very long baseline interferometry observations of active galactic nuclei have revealed asymmetric structures in the jets of radio galaxies. These asymmetric structures may be due to internal asymmetries in the jets or they may be induced by the different conditions in the surrounding ambient medium, including the obscuring torus, or a combination of the two. Aims. In this paper we investigate the influence of the ambient medium, including the obscuring torus, on the observed properties of jets from radio galaxies. Methods. We performed special-relativistic hydrodynamic (SRHD) simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code Ratpenat, which is based on a second-order accurate finite-volume method and an approximate Riemann solver. Using a newly developed radiative transfer code to compute the electromagnetic radiation, we modelled several jets embedded in various ambient medium and torus configurations and subsequently computed the non-thermal emission produced by the jet and thermal absorption from the torus. To better compare the emission simulations with observations we produced synthetic radio maps, taking into account the properties of the observatory. Results. The detailed analysis of our simulations shows that the observed properties such as core shift could be used to distinguish between over-pressured and pressure matched jets. In addition to the properties of the jets, insights into the extent and density of the obscuring torus can be obtained from analyses of the single-dish spectrum and spectral index maps. [ABSTRACT FROM AUTHOR]

Context. Precise determination of stellar masses is necessary to test the validity of pre-main-sequence (PMS) stellar evolutionary models, whose predictions are in disagreement with measurements for masses below 1.2 M⊙. To improve such a test, and based on our previous studies, we selected the ABDoradus moving group (AB Dor-MG) as the best-suited association on which to apply radio-based high-precision astrometric techniques to study binary systems. Aims. We seek to determine precise estimates of the masses of a set of stars belonging to the ABDor-MG using radio and infrared observations. Methods. We observed in phase-reference mode with the Very Large Array (VLA) at 5 GHz and with the European VLBI Network (EVN) at 8.4 GHz the stars HD160934, EKDra, PWAnd, and LO Peg. We also observed some of these stars with the near-infrared CCD AstraLux camera at the Calar Alto observatory to complement the radio observations. Results. We determine model-independent dynamical masses of both components of the star HD160934, A and c, which are 0.70 ± 0.07 M⊙ and 0.45 ± 0.04 M⊙, respectively. We revised the orbital parameters of EK Dra and we determine a sum of the masses of the system of 1.38 ± 0.08 M⊙. We also explored the binarity of the stars LO Peg and PWAnd. Conclusions. We found observational evidence that PMS evolutionary models underpredict the mass of PMS stars by 10%-40%, as previously reported by other authors. We also inferred that the origin of the radio emission must be similar in all observed stars, that is, extreme magnetic activity of the stellar corona that triggers gyrosynchrotron emission from non-thermal, accelerated electrons. [ABSTRACT FROM AUTHOR]

Aims. We started a follow-up investigation of the "Deep X-ray Radio Blazar Survey" objects with declination >-10 deg to better understand the blazar phenomenon. We undertook a survey with the European Very Long Baseline Interferometry Network at 5 GHz to make the first images of a complete sample of weak blazars, aiming at a follow-up comparison between high- and low-power samples of blazars. Methods. We observed 87 sources with the EVN at 5GHz during the period October 2009 to May 2013. The observations were correlated at the Max-Planck-Institut für Radioastronomie and at the Joint Institute for VLBI in Europe. The correlator output was analysed using both the AIPS and DIFMAP software packages. Results. All of the sources observed were detected. Point-like sources are found in 39 cases on a milli-arcsecond scale, and 48 show core-jet structure. The total flux density distribution at 5 GHz has a median value (S) = 44-10+23 mJy. A total flux density ⩽150 mJy is observed in 68 out of 87 sources. Their brightness temperature Tb ranges between 107 K and 1012 K. According to the spectral indices previously obtained with multi-frequency observations, 58 sources show a flat spectral index, and 29 sources show a steep spectrum or a spectrum peaking at a frequency around 1-2GHz. Adding to the DXRBS objects we observed those already observed with ATCA in the Southern sky, we found that 14 blazars and a Steep Spectrum Radio Quasars, are associated to γ-ray emitters. Conclusions. We found that 56 sources can be considered blazars. We also detected 2 flat spectrum narrow line radio galaxies. About 50% of the blazars associated to a γ-ray object are BL Lacs, confirming that they are more likely detected among blazars γ-emitters. We confirm the correlation found between the source core flux density and the γ-ray photon fluxes down to fainter flux densities. We also found that weak blazars are also weaker γ-ray emitters compared to bright blazars. Twenty-two sources are SSRQs or Compact Steep-spectrum Sources, and 7 are GigaHz Peaked Sources. The available X-ray ROSAT observations allow us to suggest that CSS and GPS quasars are not obscured by large column of cold gas surrounding the nuclei. We did not find any significant difference in X-ray luminosity between CSS and GPS quasars. [ABSTRACT FROM AUTHOR]

Context. Centaurus A (Cen A) is the closest radio-loud active galactic nucleus. Very Long Baseline Interferometry (VLBI) enables us to study the spectral and kinematic behavior of the radio jet-counterjet system on milliarcsecond scales, providing essential information for jet emission and propagation models. Aims. In the framework of the TANAMI monitoring, we investigate the kinematics and complex structure of Cen A on subparsec scales. We have been studying the evolution of the central parsec jet structure of CenA for over 3.5 years. The proper motion analysis of individual jet components allows us to constrain jet formation and propagation and to test the proposed correlation of increased high-energy flux with jet ejection events. Cen A is an exceptional laboratory for such a detailed study because its proximity translates to unrivaled linear resolution, where one milliarcsecond corresponds to 0.018 pc. Methods. As a target of the southern-hemisphere VLBI monitoring program TANAMI, observations of CenA are done approximately every six months at 8.4 GHz with the Australian Long Baseline Array (LBA) and associated telescopes in Antarctica, Chile, New Zealand, and South Africa, complemented by quasi-simultaneous 22.3 GHz observations. Results. The first seven epochs of high-resolution TANAMI VLBI observations at 8.4 GHz of CenA are presented, resolving the jet on (sub-)milliarcsecond scales. They show a di erential motion of the subparsec scale jet with significantly higher component speeds farther downstream where the jet becomes optically thin. We determined apparent component speeds within a range of 0:1 c to 0:3 c and identified long-term stable features. In combination with the jet-to-counterjet ratio, we can constrain the angle to the line of sight to θ ∼ 12°-45°. Conclusions. The high-resolution kinematics are best explained by a spine-sheath structure supported by the downstream acceleration occurring where the jet becomes optically thin. On top of the underlying, continuous flow, TANAMI observations clearly resolve individual jet features. The flow appears to be interrupted by an obstacle causing a local decrease in surface brightness and circumfluent jet behavior. We propose a jet-star interaction scenario to explain this appearance. The comparison of jet ejection times to high X-ray flux phases yields a partial overlap of the onset of the X-ray emission and increasing jet activity, but the limited data do not support a robust correlation. [ABSTRACT FROM AUTHOR]

The IceCube Collaboration has announced the discovery of a neutrino flux in excess of the atmospheric background. Owing to the steeply falling atmospheric background spectrum, events at PeV energies most likely have an extraterrestrial origin. We present the multiwavelength properties of the six radio-brightest blazars that are positionally coincident with these events using contemporaneous data of the TANAMI blazar sample, including high-resolution images and spectral energy distributions. Assuming the X-ray to γ-ray emission originates in the photoproduction of pions by accelerated protons, the integrated predicted neutrino luminosity of these sources is high enough to explain the two detected PeV events. [ABSTRACT FROM AUTHOR]

Aims. We use a sample of 83 core-dominated active galactic nuclei (AGN) selected from the MOJAVE (Monitoring of Jets in AGN with VLBA Experiments) radio-flux-limited sample and detected with the Fermi Large Area Telescope (LAT) to study the relations between non-simultaneous radio, optical, and γ-ray measurements. Methods. We perform a multi-band statistical analysis to investigate the relations between the emissions in different bands and reproduce these relations by modeling of the spectral energy distributions of blazars. Results. There is a significant correlation between the γ-ray luminosity and the optical nuclear and radio (15 GHz) luminosities of blazars. We report a well defined positive correlation between the γ-ray luminosity and the radio-optical loudness for quasars and BL Lacertae type objects (BL Lacs). A strong positive correlation is found between the radio luminosity and the γ-ray-optical loudness for quasars, while a negative correlation between the optical luminosity and the γ-ray-radio loudness is present for BL Lacs. Modeling of these correlations with a simple leptonic jet model for blazars indicates that variations of the accretion disk luminosity (and hence the jet power) is able to reproduce the trends observed in most of the correlations. To reproduce all observed correlations, variations of several parameters, such as the accretion power, jet viewing angle, Lorentz factor, and magnetic field of the jet, are required. [ABSTRACT FROM AUTHOR]