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Description
The third Fermi Large Area Telescope {gamma}-ray source catalog (3FGL) contains over 1000 objects for which there is no known counterpart at other wavelengths. The physical origin of the {gamma}-ray emission from those objects is unknown. Such objects are commonly referred to as unassociated and mostly do not exhibit significant {gamma}-ray flux variability. We performed a survey of all unassociated {gamma}-ray sources found in 3FGL using the Australia Telescope Compact Array and Very Large Array in the range 4.0-10.0 GHz. We found 2097 radio candidates for association with {gamma}-ray sources. The follow-up with very long baseline interferometry for a subset of those candidates yielded 142 new associations with active galactic nuclei that are {gamma}-ray sources, provided alternative associations for seven objects, and improved positions for another 144 known associations to the milliarcsecond level of accuracy. In addition, for 245 unassociated {gamma}-ray sources we did not find a single compact radio source above 2 mJy within 3{sigma} of their {gamma}-ray localization. A significant fraction of these empty fields, 39%, are located away from the Galactic plane. We also found 36 extended radio sources that are candidates for association with a corresponding {gamma}-ray object, 19 of which are most likely supernova remnants or H II regions, whereas 17 could be radio galaxies.
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