The Fermi Large Area Telescope (LAT) has now released the second catalog of high-energy gamma-ray sources (2FGL) derived from data taken during the first 24 months of the science phase of the mission. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range. Of the 1873 sources in 2FGL, 1017 sources at high Galactic latitude (abs(b) > 10 degrees) are associated statistically with active galactic nuclei (AGNs).
Parsec-scale VLBI measurements play an important role in characterizing the nature of the candidate AGNs by providing crucial extra information to improve the probability of correct identification - VLBI filters out objects which do not host strong compact jets at parsec scale. VLBI programs in both hemispheres have been underway over the past few years to monitor Fermi sources. However, current programs are somewhat limited to brighter sources, thus missing radio weak objects in the large all-sky surveys.
In this presentation, we plan to describe aspects of our VLBI monitoring program of a large number of AGNs that is carried out with NASA's Deep Space network simultaneously at 8 and 32 GHz with unparalleled angular resolution reaching source flux densities at the 25 mJy level. The goal is to obtain crucial information about parsec-scale activity in AGN cores, probing intrinsic jet parameters and providing the opportunity for discriminating between different models of gamma-ray emission in these objects.
These observations are intended to augment existing single-dish and VLBA monitoring programs. Additionally, our baselines will provide coverage for sources with declination between -20 and -40 degrees, which is a region not well covered by current VLBI programs.