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

Abstract

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+096within the VLBA-BU-BLAZAR 7mm 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 \\sr 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.