MAGIC Observations and multiwavelength properties of the quasar 3C 279 in 2007 and 2009

¹ IFAE, Edifici Cn., Campus UAB, 08193 Bellaterra, Spain
² INAF National Institute for Astrophysics, 00136 Rome, Italy
e-mail: fabrizio.tavecchio@brera.inaf.it
³ Università di Siena and INFN Pisa, 53100 Siena, Italy
⁴ Technische Universität Dortmund, 44221 Dortmund, Germany
⁵ Universidad Complutense, 28040 Madrid, Spain
⁶ Università di Padova and INFN, 35131 Padova, Italy
⁷ Inst. de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
e-mail: berger@astro.uni-wuerzburg.de
⁸ Depto. de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Spain
⁹ University of Łódź, 90236 Łódź, Poland
¹⁰ Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
e-mail: elilin@utu.fi
¹¹ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹² ETH Zurich, 8093 Switzerland
¹³ Max-Planck-Institut für Physik, 80805 München, Germany
¹⁴ Universität Würzburg, 97074 Würzburg, Germany
¹⁵ Universitat de Barcelona (ICC/IEEC), 08028 Barcelona, Spain
¹⁶ Università di Udine and INFN Trieste, 33100 Udine, Italy
¹⁷ Institut de Ciències de l’Espai (IEEC-CSIC), 08193 Bellaterra, Spain
¹⁸ Inst. de Astrofísica de Andalucía (CSIC), 18080 Granada, Spain
¹⁹ Croatian MAGIC Consortium, Institute R. Boskovic, University of Rijeka and University of Split, 10000 Zagreb, Croatia
²⁰ Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
²¹ Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
²² INAF/Osservatorio Astronomico and INFN, 34143 Trieste, Italy
²³ Università dell’Insubria, Como, 22100 Como, Italy
²⁴ Università di Pisa and INFN Pisa, 56126 Pisa, Italy
²⁵ ICREA, 08010 Barcelona, Spain
²⁶ University of California, Los Angeles, USA

Received: 11 January 2011
Accepted: 18 February 2011

Abstract

Context. 3C 279, the first quasar discovered to emit VHE γ-rays by the MAGIC telescope in 2006, was reobserved by MAGIC in January 2007 during a major optical flare and from December 2008 to April 2009 following an alert from the Fermi space telescope on an exceptionally high γ-ray state.

Aims. The January 2007 observations resulted in a detection on January 16 with significance 5.4σ, corresponding to a F (>150 GeV) (3.8 ± 0.8) × 10^-11 ph cm^-2 s^-1 while the overall data sample does not show significant signal. The December 2008–April 2009 observations did not detect the source. We study the multiwavelength behaviour of the source at the epochs of MAGIC observations, collecting quasi-simultaneous data at optical and X-ray frequencies and for 2009 also γ-ray data from Fermi.

Methods. We study the light curves and spectral energy distribution of the source. The spectral energy distributions of three observing epochs (including the February 2006, which has been previously published) are modelled with one-zone inverse Compton models and the emission on January 16, 2007 also with two zone model and with a lepto-hadronic model.

Results. We find that the VHE γ-ray emission detected in 2006 and 2007 challenges standard one-zone model, based on relativistic electrons in a jet scattering broad line region photons, while the other studied models fit the observed spectral energy distribution more satisfactorily.