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Core-Jet Blending Effects in AGN under the KVN View at 43 GHz
Juan-Carlos Algaba,Sincheol Kang,Dae-Won Kim,Jae-Young Kim,Jee Won Lee,Sang-Sung Lee,Sascha Trippe 한국천문학회 2019 Journal of The Korean Astronomical Society Vol.52 No.2
A long standing problem in the study of Active Galactic Nuclei (AGNs) is that the observed VLBI core is in fact a blending of the actual AGN core (classically defined by the tau=1 surface) and the upstream regions of the jet or optically thin flows. This blending may cause some biases in the observables of the core, such as its flux density, size or brightness temperature, which may lead to misleading interpretation of the derived quantities and physics. We study the effects of such blending under the view of the Korean VLBI Network (KVN) for a sample of AGNs at 43 GHz by comparing their observed properties with observations obtained using the Very Large Baseline Array (VLBA). Our results suggest that the observed core sizes are a factor 11 larger than these of VLBA, which is similar to the factor expected by considering the different resolutions of the two facilities. We suggest the use of this factor to consider blending effects in KVN measurements. Other parameters, such as flux density or brightness temperature, seem to possess a more complicated dependence.
PAGAN II: THE EVOLUTION OF AGN JETS ON SUB-PARSEC SCALES
OH, JUNGHWAN,TRIPPE, SASCHA,KANG, SINCHEOL,KIM, JAE-YOUNG,PARK, JONG-HO,LEE, TAESEOK,KIM, DAEWON,KINO, MOTOKI,LEE, SANG-SUNG,SOHN, BONG WON The Korean Astronomical Society 2015 Journal of The Korean Astronomical Society Vol.48 No.5
We report first results from KVN and VERA Array (KaVA) VLBI observations obtained in the frame of our Plasma-physics of Active Galactic Nuclei (PAGaN) project. We observed eight selected AGN at 22 and 43 GHz in single polarization (LCP) between March 2014 and April 2015. Each source was observed for 6 to 8 hours per observing run to maximize the uv coverage. We obtained a total of 15 deep high-resolution images permitting the identification of individual circular Gaussian jet components and three spectral index maps of BL Lac, 3C 111 and 3C 345 from simultaneous dual-frequency observations. The spectral index maps show trends in agreement with general expectations – flat core and steep jets – while the actual value of the spectral index for jets shows indications for a dependence on AGN type. We analyzed the kinematics of jet components of BL Lac and 3C 111, detecting superluminal proper motions with maximum apparent speeds of about 5c. This constrains the lower limits of the intrinsic component velocities to ~ 0.98c and the upper limits of the angle between jet and line of sight to ~20°. In agreement with global jet expansion, jet components show systematically larger diameters d at larger core distances r, following the global relation d ≈ 0.2r, albeit within substantial scatter.