VLBA23A-316

Exploring the innermost jet regions of the blazar BL Lac with the HSA and EHT

Abstract

AGN are key objects to broaden our knowledge on Black Hole and galaxy evolution, and the role of magnetic fields in this. Here we propose HSA observation (VLBA + Effelsberg +GBT) on the nearby and archetypical BL Lac object, BL Lacertae (BL Lac; 2200+420) at 3.5mm/7mm/13mm. BL Lac is now in flaring state. We propose this study in close coordination with our approved 1.3mm EHT+ALMA observation in 2023. By scheduling the 3.5mm/7mm/13mm and 1.3mm observations close in time, we can image the jet quasi-simultaneouly at a particular high spatial resolution. This will help to study the innermost jet of BLLac on subparsec scales, which is a region of moving/stationary components, whose origin still is poorly understood. BL Lac is particularly close to us (redshift~0.069) and has a bright radio jet at mm-wavebands. More importantly, the jet is highly polarized also in its innermost region close to the central black hole. This facilitates a detailed study of jet rotation measure and spectral properties with a spatial resolution of up to 1600 Schwarzschild radii. We aim to study the configuration and strength of the jet magnetic field and the physical conditions in the innermost jet regions, close to the central engine.

Investigators

Name	Institution
Mikhail Lisakov	Max-Planck-Institut für Radioastronomie; Lebedev Physical Institute
Anne-Kathrin Baczko	Max-Planck-Institut für Radioastronomie; Chalmers University Of Technology
Andrei Lobanov	Max-Planck-Institut für Radioastronomie
Thomas Krichbaum	Max-Planck-Institut für Radioastronomie
Eduardo Ros	Max-Planck-Institut für Radioastronomie; València, Universitat de
Tony Zensus	National Radio Astronomy Observatory; Max-Planck-Institut für Radioastronomie
Daewon Kim *	Max-Planck-Institut für Radioastronomie
GBT Operator	Green Bank Observatory

* indicates the PI