Contemporaneous VLBA 5 GHz Observations of LAT-Detected Blazars
  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.
