Radio and Gamma-ray Properties of Extragalactic Jets from the TANAMI Sample

TL;DR

This study analyzes the radio and gamma-ray properties of extragalactic jets from the TANAMI sample, revealing correlations between luminosities, brightness temperatures, and gamma-ray detection rates, and identifying new gamma-ray sources.

Contribution

It provides the first simultaneous radio and gamma-ray analysis of the TANAMI sample, establishing luminosity relations and Doppler boosting effects, and identifying new gamma-ray sources.

Findings

72% of sources are gamma-ray bright

Gamma-ray and radio luminosities are correlated with L_gamma ∝ L_r^0.89

Brightness temperatures above inverse Compton limit indicate strong Doppler boosting

Abstract

Using high-resolution radio imaging with VLBI techniques, the TANAMI program has been observing the parsec-scale radio jets of southern (declination south of -30{\deg}) gamma-ray bright AGN simultaneously with Fermi/LAT monitoring of their gamma-ray emission. We present the radio and gamma-ray properties of the TANAMI sources based on one year of contemporaneous TANAMI and Fermi/LAT data. A large fraction (72%) of the TANAMI sample can be associated with bright gamma-ray sources for this time range. Association rates differ for different optical classes with all BL Lacs, 76% of quasars and just 17% of galaxies detected by the LAT. Upper limits were established on the gamma-ray flux from TANAMI sources not detected by LAT. This analysis led to the identification of three new Fermi sources whose detection was later confirmed. The gamma-ray and radio luminosities are related by $L_\gamma \propto L_r^{0.89+-0.04}$. The brightness temperatures of the radio cores increase with the average gamma-ray luminosity, and the presence of brightness temperatures above the inverse Compton limit implies strong Doppler boosting in those sources. The undetected sources have lower gamma/radio luminosity ratios and lower contemporaneous brightness temperatures. Unless the Fermi/LAT-undetected blazars are strongly gamma-ray-fainter than the Fermi/LAT-detected ones, their gamma-ray luminosity should not be significantly lower than the upper limits calculated here.