Gamma-ray loudness, synchrotron peak frequency, and parsec-scale properties of blazars detected by the Fermi large area telescope

Abstract

The parsec-scale radio properties of 232 active galactic nuclei, 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 5GHz. Data from both the first 11 months (1FGL) and the first 2years (2FGL) of the Fermi mission were used to investigate these sources' γ-ray properties. We use the ratio of the γ-ray-to-radio luminosity as a measure of γ-ray loudness. We investigate the relationship of several radio properties to γ-ray loudness and to the synchrotron peak frequency. There is a tentative correlation between γ-ray loudness and synchrotron peak frequency for BLLac 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 γ-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 BLLac objects and FSRQs. The core brightness temperature also correlates with synchrotron peak frequency, but only for the BLLac objects. The low-synchrotron-peaked (LSP) BLLac object sample shows indications of contamination by FSRQs which happen to have undetectable emission lines. There is evidence that the LSP BLLac objects are more strongly beamed than the rest of the BLLac object population. © 2012. The American Astronomical Society. All rights reserved.