Identification of gamma-ray emission from 3C345 and NRAO512
  For more than 15 years, since the days of the Energetic Gamma-Ray Experiment
Telescope (EGRET) on board the Compton Gamma-Ray Observatory (CGRO; 1991-2000),
it has remained an open question why the prominent blazar 3C 345 was not
reliably detected at gamma-ray energies <=20 MeV. Recently a bright gamma-ray
source (0FGL J1641.4+3939/1FGL J1642.5+3947), potentially associated with 3C
345, was detected by the Large Area Telescope (LAT) on Fermi. Multiwavelength
observations from radio bands to X-rays (mainly GASP-WEBT and Swift) of
possible counterparts (3C 345, NRAO 512, B3 1640+396) were combined with 20
months of Fermi-LAT monitoring data (August 2008 - April 2010) to associate and
identify the dominating gamma-ray emitting counterpart of 1FGL J1642.5+3947.
The source 3C 345 is identified as the main contributor for this gamma-ray
emitting region. However, after November 2009 (15 months), a significant excess
of photons from the nearby quasar NRAO 512 started to contribute and thereafter
was detected with increasing gamma-ray activity, possibly adding flux to 1FGL
J1642.5+3947. For the same time period and during the summer of 2010, an
increase of radio, optical and X-ray activity of NRAO 512 was observed. No
gamma-ray emission from B3 1640+396 was detected.
