Y. Y. Kovalev

Catching the radio flare in CTA 102 - II. VLBI kinematic analysis

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 CTA 102 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 CTA 102 (Paper I). Methods. In this paper we study the kinematics of CTA 102 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 15 GHz and 43 GHz. Results. We cross-identified seven features throughout our entire multifrequency observations and find evidence of two possible recollimation shocks around 0.1 mas (deprojected 18 pc at a viewing angle ϑ = 2.6 ◦ )a nd 6.0 mas (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.

Very Long Baseline Interferometry with the SKA

Adding VLBI capability to the SKA arrays will greatly broaden the science of the SKA, and is feasible within the current specifications. SKA-VLBI can be initially implemented by providing phased-array outputs for SKA1-MID and SKA1-SUR and using these extremely sensitive stations with other radio telescopes, and in SKA2 by realising a distributed configuration providing baselines up to thousands of km, merging it with existing VLBI networks. The motivation for and the possible realization of SKA-VLBI is described in this paper.

Very Long Baseline polarimetry and the γ-ray connection in Markarian 421 during the broadband campaign in 2011

Context. This is the third paper in a series devoted to the analysis of the multiwavelength data from a campaign on the nearby (z = 0.03) TeV blazar Mrk 421 during 2011. Aims. We investigate the structure of the high angular resolution polarization, the magnetic topology, the total intensity light curve, the γ-ray flux, and the photon index. We describe how they evolve and how they are connected. Methods. We analyzed data in polarized intensity obtained with the Very Long Baseline Array (VLBA) at twelve epochs (one observation per month from January to December 2011) at 15, 24, and 43 GHz. For the absolute orientation of the electric vector position angles (EVPA) we used the D-terms method; we also confirm its accuracy. We also used γ-ray data from the Fermi Large Area Telescope on weekly time bins throughout 2011. Results. The source shows polarized emission, and its properties vary with time, frequency, and location along the jet. The core mean polarization fraction is generally between 1% and 2%, with a 4% peak at 43 GHz in March; the polarization angle is variable, mainly at 15 GHz, where it changes frequently, and less so at 43 GHz, where it oscillates in the range 114 ◦ −173 ◦ . The jet polarization properties are more stable, with a fractional polarization of around 16% and a polarization angle nearly perpendicular to the jet axis. The average flux and photon index at γ-ray energies are (17.4 ± 0.5) ×10 −8 ph cm −2 s −1 and Γ= 1.77 ± 0.02. The γ-ray light curve shows variability, with a main peak of (38 ± 11) × 10 −8 ph cm −2 s −1 at the beginning of March and two later peaks centered on September 8 and November 13. The first γ-ray peak appears to be associated with the peak in the core polarized emission at 43 GHz, as well as with the total intensity light curve. A discrete correlation function analysis yields a correlation coefficient of 0.54 at zero delay, with a significance level >99.7%. Conclusions. With this multifrequency study, we accurately determine the polarization properties of Mrk 421, both in the core and in the jet region. The radio and γ-ray light curves are correlated. The observed EVPA variability at 15 GHz is partly due to opacity and partly to a variable Faraday rotation effect. To explain the residual variability of the intrinsic polarization angle and the low degree of polarization in the core region, we invoke a blend of variable cross-polarized subcomponents with different polarization properties within the beam.

Properties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies (Corrigendum)

We report about recent updates of broad-band properties of radio-loud narrow-line Seyfert 1 galaxies.

Erratum: Sub-milliarcsecond imaging of quasars and active galactic nuclei. IV. Fine-scale structure (The Astronomical Journal (2005) 130 (2473))

The limit flag on theminor core axis FWHM, min, was incorrectly shown as ‘‘>’’ in themachine-readable version of Table 2, position 51. It should be ‘‘<,’’ indicating an upper limit of min for all the cases in which the limit is defined. The printed version and HTML version of Table 2 are correct as published. This correction of the machine-readable version of Table 2 is only typographical in nature, and none of the results in the paper were affected. Online material: machine-readable table

Global millimeter VLBI array survey of ultracompact extragalactic radio sources at 86 GHz

Very Long Baseline Interferometry (VLBI) observations at 86 GHz (

ERRATUM: “MOJAVE: MONITORING OF JETS IN ACTIVE GALACTIC NUCLEI WITH VLBA EXPERIMENTS. VI. KINEMATICS ANALYSIS OF A COMPLETE SAMPLE OF BLAZAR JETS” (2009, AJ, 138, 1874)

\sim 3

ERRATUM: “MOJAVE: MONITORING OF JETS IN AGN WITH VLBA EXPERIMENTS. V. MULTI-EPOCH VLBA IMAGES” (2009, AJ, 137, 3718)

mm) reach a resolution of about 50 micro arcsec and sample the scales as small as

Apparent parsec-scale jet opening angles and \gamma-ray brightness of active galactic nuclei

10^{3}-10^{4}

Multi-frequency study of the TeV blazar Markarian 421 with VLBA observations taken during 2011

Schwarzschild radii of the central black hole in Active Galactic Nuclei (AGN), and uncover the jet regions where acceleration and collimation of the relativistic flow takes place. We present results from a large global 86 GHz VLBI survey of 162 ultra compact radio sources conducted in 2010-2011 using the Global Millimeter VLBI Array (GMVA). This survey has contributed an increase of