# Core-Jet Blending Effects in Active Galactic Nuclei under the Korean VLBI Network View at 43 GHz

## TL;DR

This study investigates how blending of the true AGN core with upstream jet regions affects VLBI measurements at 43 GHz, using KVN and VLBA data, revealing significant core size biases and complex flux-related effects.

## Contribution

It provides a comparative analysis of core blending effects in AGN observations between KVN and VLBA, highlighting the impact on measured core sizes and suggesting correction factors.

## Key findings

- Observed core sizes are about 11 times larger in KVN than VLBA, consistent with resolution differences.
- Blending effects significantly bias core size measurements in KVN data.
- Flux density and brightness temperature show complex dependence on blending effects.

## Abstract

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 emitting region flows. This blending may cause some biases towards 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 with the Very Large Baseline Array (VLBA). Our results suggest that the observed core sizes are a factor $\sim11$ 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.