The Point of Origin of the Radio Radiation from the Unresolved Cores of Radio-Loud Quasars

Locating the exact point of origin of the core radiation in active galactic nuclei (AGN) would represent important progress in our understanding of physical processes in the central engine of these objects. However, due to our inability to resolve the region containing both the central compact object and the jet base, this has so far been difficult. Here, using an analysis in which the lack of resolution does not play a significant role, we demonstrate that it may be impossible even in most radio loud sources for more than a small percentage of the core radiation at radio wavelengths to come from the jet base. We find for 3C279 that $\sim85$ percent of the core flux at 15 GHz must come from a separate, reasonably stable, region that is not part of the jet base, and that then likely radiates at least quasi-isotropically and is centered on the black hole. The long-term stability of this component also suggests that it may originate in a region that extends over many Schwarzschild radii.Comment: 7 pages with 3 figures, accepted for publication in Astrophysics and Space Scienc

Correlations between the peak flux density and the position angle of inner-jet in three blazars

We aim to investigate the relation between the long-term flux density and the position angle (PA) evolution of inner-jet in blazars. We have carried out the elliptic Gaussian model-fit to the `core' of 50 blazars from 15 GHz VLBA data, and analyzed the variability properties of three blazars from the model-fit results. Diverse correlations between the long-term peak flux density and the PA evolution of the major axis of the `core' have been found in $\sim$ 20% of the 50 sources. Of them, three typical blazars have been analyzed, which also show quasi-periodic flux variations of a few years (T). The correlation between the peak flux density and the PA of inner-jet is positive for S5~0716+714, and negative for S4~1807+698. The two sources cannot be explained with the ballistic jet models, the non-ballistic models have been analyzed to explain the two sub-luminal blazars. A correlation between the peak flux density and the PA (with a T/4 time lag) of inner-jet is found in [HB89]~1823+568, this correlation can be explained with a ballistic precession jet model. All the explanations are based mainly on the geometric beaming effect; physical flux density variations from the jet base would be considered for more complicated situations in future, which could account for the no or less significance of the correlation between the peak flux density and the PA of inner-jet in the majority blazars of our sample.Comment: 6 pages, 7 figures, accepted for publication in Astrophysics and Space Scienc

Extragalactic Relativistic Jets and Nuclear Regions in Galaxies

Past years have brought an increasingly wider recognition of the ubiquity of relativistic outflows (jets) in galactic nuclei, which has turned jets into an effective tool for investigating the physics of nuclear regions in galaxies. A brief summary is given here of recent results from studies of jets and nuclear regions in several active galaxies with prominent outflows.Comment: 5 pages; contribution to ESO Astrophysical Symposia, "Relativistic Astrophysics and Cosmology", eds. B. Aschenbach, V. Burwitz, G. Hasinger, B. Leibundgut (Springer: Heidelberg 2006

Active Galactic Nuclei at the Crossroads of Astrophysics

Over the last five decades, AGN studies have produced a number of spectacular examples of synergies and multifaceted approaches in astrophysics. The field of AGN research now spans the entire spectral range and covers more than twelve orders of magnitude in the spatial and temporal domains. The next generation of astrophysical facilities will open up new possibilities for AGN studies, especially in the areas of high-resolution and high-fidelity imaging and spectroscopy of nuclear regions in the X-ray, optical, and radio bands. These studies will address in detail a number of critical issues in AGN research such as processes in the immediate vicinity of supermassive black holes, physical conditions of broad-line and narrow-line regions, formation and evolution of accretion disks and relativistic outflows, and the connection between nuclear activity and galaxy evolution.Comment: 16 pages, 5 figures; review contribution; "Exploring the Cosmic Frontier: Astrophysical Instruments for the 21st Century", ESO Astrophysical Symposia Serie

Experimental vertical stability studies for ITER performance and design

Operating experimental devices have provided key inputs to the design process for ITER axisymmetric control. In particular, experiments have quantified controllability and robustness requirements in the presence of realistic noise and disturbance environments, which are difficult or impossible to characterize with modelling and simulation alone. This kind of information is particularly critical for ITER vertical control, which poses the highest demands on poloidal field system performance, since the consequences of loss of vertical control can be severe. This work describes results of multi-machine studies performed under a joint ITPA experiment (MDC-13) on fundamental vertical control performance and controllability limits. We present experimental results from Alcator C-Mod, DIII-D, NSTX, TCV and JET, along with analysis of these data to provide vertical control performance guidance to ITER. Useful metrics to quantify this control performance include the stability margin and maximum controllable vertical displacement. Theoretical analysis of the maximum controllable vertical displacement suggests effective approaches to improving performance in terms of this metric, with implications for ITER design modifications. Typical levels of noise in the vertical position measurement and several common disturbances which can challenge the vertical control loop are assessed and analysed.United States Department of Energy (DE-FC02-04ER54698, DEAC52- 07NA27344, and DE-FG02-04ER54235

Gamma-Ray and Parsec-Scale Jet Properties of a Complete Sample of Blazars from the MOJAVE Program

We investigate the Fermi LAT gamma-ray and 15 GHz VLBA radio properties of a joint gamma-ray- and radio-selected sample of AGNs obtained during the first 11 months of the Fermi mission (2008 Aug 4 - 2009 Jul 5). Our sample contains the brightest 173 AGNs in these bands above declination -300 during this period, and thus probes the full range of gamma-ray loudness (gamma-ray to radio band luminosity ratio) in the bright blazar population. The latter quantity spans at least four orders of magnitude, reflecting a wide range of spectral energy distribution (SED) parameters in the bright blazar population. The BL Lac objects, however, display a linear correlation of increasing gamma-ray loudness with synchrotron SED peak frequency, suggesting a universal SED shape for objects of this class. The synchrotron self-Compton model is favored for the gamma-ray emission in these BL Lacs over external seed photon models, since the latter predict a dependence of Compton dominance on Doppler factor that would destroy any observed synchrotron SED peak - gamma-ray loudness correlation. The high-synchrotron peaked (HSP) BL Lac objects are distinguished by lower than average radio core brightness temperatures, and none display large radio modulation indices or high linear core polarization levels. No equivalent trends are seen for the flat-spectrum radio quasars (FSRQ) in our sample. Given the association of such properties with relativistic beaming, we suggest that the HSP BL Lacs have generally lower Doppler factors than the lower-synchrotron peaked BL Lacs or FSRQs in our sample

Modelling spectral and timing properties of accreting black holes: the hybrid hot flow paradigm

The general picture that emerged by the end of 1990s from a large set of optical and X-ray, spectral and timing data was that the X-rays are produced in the innermost hot part of the accretion flow, while the optical/infrared (OIR) emission is mainly produced by the irradiated outer thin accretion disc. Recent multiwavelength observations of Galactic black hole transients show that the situation is not so simple. Fast variability in the OIR band, OIR excesses above the thermal emission and a complicated interplay between the X-ray and the OIR light curves imply that the OIR emitting region is much more compact. One of the popular hypotheses is that the jet contributes to the OIR emission and even is responsible for the bulk of the X-rays. However, this scenario is largely ad hoc and is in contradiction with many previously established facts. Alternatively, the hot accretion flow, known to be consistent with the X-ray spectral and timing data, is also a viable candidate to produce the OIR radiation. The hot-flow scenario naturally explains the power-law like OIR spectra, fast OIR variability and its complex relation to the X-rays if the hot flow contains non-thermal electrons (even in energetically negligible quantities), which are required by the presence of the MeV tail in Cyg X-1. The presence of non-thermal electrons also lowers the equilibrium electron temperature in the hot flow model to <100 keV, making it more consistent with observations. Here we argue that any viable model should simultaneously explain a large set of spectral and timing data and show that the hybrid (thermal/non-thermal) hot flow model satisfies most of the constraints.Comment: 26 pages, 13 figures. To be published in the Space Science Reviews and as hard cover in the Space Sciences Series of ISSI - The Physics of Accretion on to Black Holes (Springer Publisher

Measurement of the polarisation of W bosons produced with large transverse momentum in pp collisions at sqrt(s) = 7 TeV with the ATLAS experiment

This paper describes an analysis of the angular distribution of W->enu and W->munu decays, using data from pp collisions at sqrt(s) = 7 TeV recorded with the ATLAS detector at the LHC in 2010, corresponding to an integrated luminosity of about 35 pb^-1. Using the decay lepton transverse momentum and the missing transverse energy, the W decay angular distribution projected onto the transverse plane is obtained and analysed in terms of helicity fractions f0, fL and fR over two ranges of W transverse momentum (ptw): 35 < ptw < 50 GeV and ptw > 50 GeV. Good agreement is found with theoretical predictions. For ptw > 50 GeV, the values of f0 and fL-fR, averaged over charge and lepton flavour, are measured to be : f0 = 0.127 +/- 0.030 +/- 0.108 and fL-fR = 0.252 +/- 0.017 +/- 0.030, where the first uncertainties are statistical, and the second include all systematic effects.Comment: 19 pages plus author list (34 pages total), 9 figures, 11 tables, revised author list, matches European Journal of Physics C versio