Contemporaneous VLBA 5 GHz Observations of LAT-Detected Blazars

TL;DR

This study uses contemporaneous VLBA 5 GHz observations of 232 LAT-detected blazars to explore the connection between radio properties and gamma-ray emission, revealing correlations with magnetic fields and polarization.

Contribution

It provides the largest flux-limited sample of AGN with simultaneous radio and gamma-ray data, highlighting differences between LAT and non-LAT sources and the role of magnetic fields.

Findings

Gamma-ray emission correlates with strong, uniform magnetic fields in AGN cores.

LAT blazars show higher core polarization and increased polarization during detection.

LAT FSRQs differ significantly from non-LAT FSRQs in radio properties.

Abstract

The radio properties of 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). In total, 232 sources were observed with the VLBA. Ninety sources that were previously observed as part of the VLBA Imaging and Polarimetry Survey (VIPS) have been included in the sample, as well as 142 sources not found in VIPS. This very large, flux-limited sample of active galactic nuclei (AGN) provides insights into the mechanism that produces strong gamma-ray emission. In particular, we see that gamma-ray emission is related to strong, uniform magnetic fields in the cores of the host AGN. Included in this sample are non-blazar AGN such as 3C84, M82, and NGC 6251. For the blazars, the total VLBA radio flux density at 5 GHz correlates strongly with gamma-ray flux. The LAT BL Lac objects tend to be similar to the non-LAT BL Lac objects, but the LAT flat-spectrum radio quasars (FSRQs) are significantly different from the non-LAT FSRQs. Strong core polarization is significantly more common among the LAT sources, and core fractional polarization appears to increase during LAT detection.