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Identification of gamma-ray emission from 3C 345 and NRAO 512

ASTRONOMY & ASTROPHYSICS 532 10.1051/0004-6361/201016145 AUG 2011

Authors:
Schinzel, FK; Sokolovsky, KV; D'Ammando, F; Burnett, TH; Max-Moerbeck, W; Cheung, CC; Fegan, SJ; Casandjian, JM; Reyes, LC; Villata, M; Raiteri, CM; Agudo, I; Calle, OJAB; Carosati, D; Casas, R; Gomez, JL; Gurwell, MA; Hsiao, HY; Jorstad, SG; Kimeridze, G; Konstantinova, TS; Kopatskaya, EN; Koptelova, E; Kurtanidze, OM; Kurtanidze, SO; Larionov, VM; Larionova, EG; Larionova, LV; Marscher, AP; Morozova, DA; Nikolashvili, MG; Roca-Sogorb, M; Ros, JA; Sigua, LA; Spiridonova, O; Troitsky, IS; Vlasyuk, VV; Lobanov, AP; Zensus, JA

Abstract:
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, NRAO512, 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 NRAO512 started to contribute a! nd 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 NRAO512 was observed. No gamma-ray emission from B3 1640+396 was detected.

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