Resolving the inner jet of PKS 1749+096 with super-resolution VLBA images at 7 mm

High resolution imaging of inner jets in Active Galactic Nuclei(AGNs)with Very Long Baseline Interferometry(VLBI)at millimeter wavelengths provides deep insight into the launching and collimation mechanisms of relativistic jets.The BL Lac object,PKS 1749+096,shows a core-dominated jet pointing toward the northeast on parsec-scales revealed by various VLBI observations.In order to investigate the jet kinematics,in particular,the orientation of the inner jet on the smallest accessible scales and the basic physical conditions of the core,in this work we adopted a super-resolution technique,the Bi-Spectrum Maximum Entropy Method(BSMEM),to reanalyze VLBI images based on the Very Long Baseline Array(VLBA)observations of PKS 1749+096 within the VLBA-BU-BLAZAR 7 mm monitoring program.These observations include a total of 105 epochs covering the period from 2009 to 2019.We found that the stacked image of the inner jet is limb-brightened with an apparent opening angle of 50°.0±8°.0 and 42°.0±6°.0 at the distances of 0.2 and 0.3 mas(0.9 and 1.4 pc)from the core,corresponding to an intrinsic jet opening angle of 5°.2±1°.0 and 4°.3±0°.7,respectively.In addition,our images show a clear jet position angle swing in PKS 1749+096 within the last ten years.We discuss the possible implications of jet limb brightening and the connection of the position angle with jet peak flux density and gamma-ray brightness.

East Asian VLBI Network observations of active galactic nuclei jets:imaging with KaVA+Tianma+Nanshan

The East Asian Very Long Baseline Interferometry(VLBI) Network(EAVN) is a rapidly evolving international VLBI array that is currently promoted under joint efforts among China,Japan and Korea.EAVN aims at forming a joint VLBI Network by combining a large number of radio telescopes distributed over East Asian regions.After the combination of the Korean VLBI Network(KVN) and the VLBI Exploration of Radio Astrometry(VERA) into Ka VA,further expansion with the joint array in East Asia is actively promoted.Here we report the first imaging results(at 22 and 43 GHz) of bright radio sources obtained with Ka VA connected to Tianma 65-m and Nanshan 26-m Radio Telescopes in China.To test the EAVN imaging performance for different sources,we observed four active galactic nuclei(AGN) having different brightness and morphology.As a result,we confirmed that the Tianma 65-m Radio Telescope(TMRT) significantly enhances the overall array sensitivity,a factor of 4 improvement in baseline sensitivity and 2 in image dynamic range compared to the case of Ka VA only.The addition of the Nanshan 26-m Radio Telescope(NSRT) further doubled the east-west angular resolution.With the resulting high-dynamic-range,high-resolution images with EAVN(Ka VA+TMRT+NSRT),various fine-scale structures in our targets,such as the counter-jet in M87,a kink-like morphology of the 3 C 273 jet and the weak emission in other sources are successfully detected.This demonstrates the powerful capability of EAVN to study AGN jets and to achieve other science goals in general.Ongoing expansion of EAVN will further enhance the angular resolution,detection sensitivity and frequency coverage of the network.

The dying accretion and jet in a powerful radio galaxy of Hercules A

Hercules A(Her A)is one of a rare class of dying and transition-type objects,which has a pair of giant,powerful radio lobes and a weak radio core.We reduce and analyze the radio data of Her A that were observed by the Expanded Very Large Array(EVLA)during 2010-2011 at C band.The intensity distribution is very smooth along the edge of the lobe front and the intensity also sharply decreases at the edge,which supports that magnetic fields may play an important role in radio lobes.The spectrum of the weak core is very steep and the core flux becomes weaker by about ten percent when compared to what was observed twenty years ago,which suggest that the central engine is still dying quickly.Her A deviates a lot from the relation between[O III]luminosity and low-frequency 178 MHz luminosity(LO III-L178 MHz)as defined by other FR I/II sources.However,when only radio core emission is considered,it roughly follows an LO III-L178 MHzcorrelation.This result supports that the black-hole accretion and large-scale jet in Her A did not evolve simultaneously,and indicates that although the large-scale jet is still powerful,the accretion and inner jet have changed into an inactive state.Based on the estimated Bondi accretion rate,we model the spectrum of Her A with a radiatively inefficient accretion flow and jet model.