Interferometric Monitoring of Gamma-ray Bright Active Galactic Nuclei II: Frequency Phase Transfer

TL;DR

This paper assesses the effectiveness of frequency phase transfer in enhancing high-frequency VLBI observations of gamma-ray bright AGN, enabling imaging of weaker sources under less-than-ideal conditions.

Contribution

It demonstrates that frequency phase transfer is viable for iMOGABA, improving coherence time and source detection at 86 and 129 GHz.

Findings

Frequency phase transfer extends coherence time at high frequencies.

The technique allows imaging of sources not detectable with standard methods.

It remains effective even under suboptimal weather conditions.

Abstract

The Interferometric Monitoring of Gamma-ray Bright Active galactic nuclei (iMOGABA) program provides not only simultaneous multifrequency observations of bright gamma-ray detected active galactic nuclei (AGN), but also covers the highest Very Large Baseline Interferometry (VLBI) frequencies ever being systematically monitored, up to 129 GHz. However, observation and imaging of weak sources at the highest observed frequencies is very challenging. In the second paper in this series, we evaluate the viability of the frequency phase transfer technique to iMOGABA in order to obtain larger coherence time at the higher frequencies of this program (86 and 129 GHz) and image additional sources that were not detected using standard techniques. We find that this method is applicable to the iMOGABA program even under non-optimal weather conditions.