Gamma-ray Loudness, Synchrotron Peak Frequency, and Parsec-Scale Properties of Blazars Detected by the Fermi Large Area Telescope

TL;DR

This study examines the radio and gamma-ray properties of blazars detected by Fermi LAT, revealing correlations between gamma-ray loudness, synchrotron peak frequency, and parsec-scale jet characteristics, with implications for blazar classification and beaming.

Contribution

It provides new insights into the relationship between gamma-ray loudness, synchrotron peak frequency, and parsec-scale jet properties of blazars using VLBA and Fermi data.

Findings

Tentative correlation between gamma-ray loudness and synchrotron peak frequency.

Correlation between VLBA flux density and synchrotron peak frequency.

Evidence of stronger beaming in low-synchrotron peaked BL Lac objects.

Abstract

The parsec-scale radio properties of 232 active galactic nuclei (AGNs), most of which are blazars, detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed contemporaneously by the Very Long Baseline Array (VLBA) at 5 GHz. Data from both the first 11 months (1FGL) and the first 2 years (2FGL) of the Fermi mission were used to investigate these sources' gamma-ray properties. We use the ratio of the gamma-ray to radio luminosity as a measure of gamma-ray loudness. We investigate the relationship of several radio properties to gamma-ray loudness and to the synchrotron peak frequency. There is a tentative correlation between gamma-ray loudness and synchrotron peak frequency for BL Lac objects in both 1FGL and 2FGL, and for flat-spectrum radio quasars (FSRQs) in 2FGL. We find that the apparent opening angle tentatively correlates with gamma-ray loudness for FSRQs, but only when we use the 2FGL data. We also find that the total VLBA flux density correlates with the synchrotron peak frequency for BL Lac objects and FSRQs. The core brightness temperature also correlates with synchrotron peak frequency, but only for the BL Lac objects. The low-synchrotron peaked (LSP) BL Lac object sample shows indications of contamination by FSRQs which happen to have undetectable emission lines. There is evidence that the LSP BL Lac objects are more strongly beamed than the rest of the BL Lac object population.