ATCA monitoring of gamma-ray loud AGN

TL;DR

This paper presents a radio monitoring program of gamma-ray loud AGN using ATCA, providing unique dynamic spectra to study the connection between radio and gamma-ray emissions in AGN jets.

Contribution

It introduces a systematic radio spectral monitoring of a large sample of AGN, many with only available data from this program, to explore emission mechanisms.

Findings

Most AGN in the sample detected by Fermi/LAT.

The program provides the only dynamic radio spectra for many sources.

Spectral index variations over time are analyzed to understand emission processes.

Abstract

As a critical part of the Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry (TANAMI) program, in November 2007 the Australia Telescope Compact Array (ATCA) started monitoring the radio spectra of a sample of southern hemisphere active galactic nuclei (AGN) that were selected as likely candidates for detection (as well as a control sample) by the Large Area Telescope (LAT) aboard the Fermi Gamma Ray Space Observatory. The initial sample was chosen based on properties determined from AGN detections by the Energetic Gamma Ray Experiment Telescope (EGRET). Most of the initial sample has been detected by Fermi/LAT and with the addition of new detections the sample has grown to include 226 AGN, 133 of which have data for more than one epoch. For the majority of these AGN, our monitoring program provides the only dynamic radio spectra available. The ATCA receiver suite makes it possible to observe several sources at frequencies between 4.5 and 41 GHz in a few hours, resulting in an excellent measure of spectral index at each epoch. By examining how the spectral index changes over time, we aim to investigate the mechanics of radio and gamma-ray emission from AGN jets.