Opacity in parsec-scale jets of active galactic nuclei: VLBA study from 1.4 to 15 GHz

TL;DR

This study investigates the frequency-dependent opacity effects in parsec-scale jets of active galactic nuclei using VLBA observations across 1.4 to 15 GHz, aiming to improve understanding of jet physics and structure.

Contribution

It provides new multi-frequency VLBA measurements of core shifts in AGN jets, extending previous work to a broader frequency range for better physical insights.

Findings

Measured core shifts between 1.4 and 15.4 GHz in AGN jets.

Demonstrated the importance of accounting for opacity effects in jet studies.

Provided initial results for a larger sample of AGNs.

Abstract

In extragalactic jets, the apparent position of the bright/narrow end (the core) depends on the observing frequency, owing to synchrotron self-absorption and external absorption. The effect must be taken into account in order to achieve unbiased results from multi-frequency VLBI data on AGN jets. Multi-frequency core shift measurements supplemented by other data enable estimating the absolute geometry and a number of fundamental physical properties of the jets and their environment. We have previously measured the shift between 13 and 3.6 cm in a sample of 29 AGNs to range between 0 and 1.4 mas. In these proceedings, we present and discuss first results of our follow-up study using VLBA between 1.4 and 15.4 GHz.