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Published April 2013 | Published
Journal Article Open

Radio to gamma-ray variability study of blazar S5 0716+714


We present the results of a series of radio, optical, X-ray, and γ-ray observations of the BL Lac object S50716+714 carried out between April 2007 and January 2011. The multifrequency observations were obtained using several ground- and space-based facilities. The intense optical monitoring of the source reveals faster repetitive variations superimposed on a long-term variability trend on a time scale of ~350 days. Episodes of fast variability recur on time scales of ~60−70 days. The intense and simultaneous activity at optical and γ-ray frequencies favors the synchrotron self-Compton mechanism for the production of the high-energy emission. Two major low-peaking radio flares were observed during this high optical/γ-ray activity period. The radio flares are characterized by a rising and a decaying stage and agrees with the formation of a shock and its evolution. We found that the evolution of the radio flares requires a geometrical variation in addition to intrinsic variations of the source. Different estimates yield robust and self-consistent lower limits of δ ≥ 20 and equipartition magnetic field B_eq ≥ 0.36 G. Causality arguments constrain the size of emission region θ ≤ 0.004 mas. We found a significant correlation between flux variations at radio frequencies with those at optical and γ-rays. Theoptical/GeV flux variations lead the radio variability by ~65 days. The longer time delays between low-peaking radio outbursts and optical flares imply that optical flares are the precursors of radio ones. An orphan X-ray flare challenges the simple, one-zone emission models, rendering them too simple. Here we also describe the spectral energy distribution modeling of the source from simultaneous data taken through different activity periods.

Additional Information

© 2013 ESO. Article published by EDP Sciences. Received 8 January 2013; Accepted 29 January 2013. Published online 13 March 2013. The Fermi/LAT Collaboration acknowledges the generous support of a number of agencies and institutes that have supported the Fermi/LAT Collaboration. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l'Énergie 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. This research is partly based on observations with the 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg. This work has made use of observations with the IRAM 30-m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). 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. The observations made use of the Noto telescope operated by INAF − Istituto di Radioastronomia. B.R. gratefully acknowledges the travel support the COSPAR Capacity-Building Workshop fellowship program. I.N. was 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. N.M. is funded by an ASI fellowship under contract number I/005/11/0. We also acknowledge the Swift Team and the Swift/XRT monitoring program efforts, as well as analysis supported by NASA Fermi GI grants NNX10AU14G. L.X. is supported by the National Natural Science Foundation of China (No. 11273050). Work at UMRAO has been supported by a series of grants from the NSF and from NASA. Support for operation of the observatory was provided by the University of Michigan. I.A. acknowledges funding by the "Consejería de Economía, Innovación y Ciencia" of the Regional Government of Andalucía through grant P09-FQM-4784, an by the "Ministerio de Economía y Competitividad" of Spain through grant AYA2010-14844. The Metsähovi team acknowledges the support from the Academy of Finland to our observing projects (numbers 212656, 210338, 121148, and others). We thank Ivan Agudo for his contribution at the 30 m telescope and for discussion. We would like to thank Marcello Giroletti, the internal referee from Fermi/LAT team for his useful suggestions and comments. We thank the referee for several helpful suggestions. We would also like to thank Jeff Hodgson for the help in finalizing the text.

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