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Published August 2011 | Published
Journal Article Open

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

Schinzel, F. K. ORCID icon
Max-Moerbeck, W. ORCID icon

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 γ-ray energies ≥ 20 MeV. Recently a bright γ-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 γ-ray emitting counterpart of 1FGL J1642.5+3947. The source 3C 345 is identified as the main contributor for this γ-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 γ-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 γ-ray emission from B3   1640 + 396 was detected.

Additional Information

© 2011 ESO. Received 15 November 2010. Accepted 7 July 2011. Published online 09 August 2011. The authors would like to thank Ann Wehrle, Benoit Lott, Seth Digel, Gino Tosti, Dave Thompson, and Greg Taylor for their helpful comments and useful discussions, which improved the quality of this manuscript. We thank the A&A referee for extensive comments. The Fermi-LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d'Etudes Spatiales in France. Frank Schinzel and Kirill Sokolovsky were supported for this research through a stipend from the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Universities of Bonn and Cologne. M. Villata organized the optical-to-radio observations by GASPWEBT as the president of the collaboration. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d'Études Spatiales in France. The St. Petersburg University team acknowledges support from Russian RFBR foundation via grant 09-02-00092. Acquisition of the MAPCAT data is supported in part by the Spanish Ministry of Science and Innovation and the Regional Government of Andalucía through grants AYA2007-67626- C03-03 and P09-FQM-4784, respectively. The Abastumani team acknowledges financial support by the Georgian National Science Foundation through grant GNSF/ST08/4-404. A. Marscher and S. Jorstad received support for this work from NASA grants NNX08AV65G, NNX08AV61G, and NNX09AT99G, and National Science Foundation grant AST-0907893 to Boston University. The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica. This paper is partly based on observations carried out at the German-Spanish Calar Alto Observatory, which is jointly operated by the MPIA and the IAACSIC. This research has made use of NASA's Astrophysics Data System, the SIMBAD database, operated at CDS, Strasbourg, France and the NASA/IPAC Extragalactic Database (NED) which is operated by the JPL, Caltech, under contract with NASA. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2009).

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