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

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69 53121 Bonn, Germany
e-mail: schinzel@mpifr-bonn.mpg.de
² Astro Space Center of Lebedev Physical Institute, Profsoyuznaya Str. 84/32, 117997 Moscow, Russia
³ INAF-IASF Palermo, 90146 Palermo, Italy
⁴ INAF-IASF Roma, 00133 Roma, Italy
⁵ Department of Physics, University of Washington, Seattle, WA 98195-1560, USA
⁶ Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125, USA
⁷ National Research Council Research Associate, National Academy of Sciences, Washington, DC 20001, resident at Naval Research Laboratory, Washington, DC 20375, USA
⁸ Laboratoire Leprince-Ringuet, École polytechnique, Route de Saclay, 91128 Palaiseau, France
⁹ Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France
¹⁰ Kavli Institute for Cosmological Physics, University of Chicago, Chicago, IL 60637, USA
¹¹ INAF - Osservatorio Astronomico di Torino, 10025 Pino Torinese (TO), Italy
¹² Institute for Astrophysical Research, Boston University, Boston, MA 02215, USA
¹³ Instituto de Astrofísica de Andalucía, CSIC, 18080 Granada, Spain
¹⁴ Astronomical Institute, St. Petersburg State University, St. Petersburg, Russia
¹⁵ EPT Observatories, Tijarafe, La Palma, Spain
¹⁶ INAF, TNG Fundación Galileo Galilei, La Palma, Spain
¹⁷ Institut de Ciencies de l’Espai (IEEC-CSIC), Campus UAB, 08193 Barcelona, Spain
¹⁸ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
¹⁹ Graduate Institute of Astronomy, National Central University, Jhongli 32054, Taiwan
²⁰ Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia
²¹ Isaac Newton Institute of Chile, St. Petersburg Branch, St. Petersburg, Russia
²² Pulkovo Astronomical Observatory, Pulkovskoe Chaussee 65/1, 196140 St. Petersburg, Russia
²³ Agrupació Astronòmica de Sabadell, 08206 Sabadell, Spain
²⁴ Special Astrophysical Observatory, Nizhnij Arkhyz, Karachai-Cherkessian Republic, 369167, Russia

Received: 15 November 2010
Accepted: 7 July 2011

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.