Multi-wavelength characterization of the blazar S5 0716+714 during an unprecedented outburst phase^⋆

¹ ETH Zurich, 8093 Zurich, Switzerland
² Università di Udine ; INFN Trieste, 33100 Udine, Italy
³ National Institute for Astrophysics (INAF), 00136 Rome, Italy
⁴ Università di Padova, Italy
⁵ Technische Universität Dortmund, 44221 Dortmund, Germany
⁶ Croatian MAGIC Consortium: University of Rijeka, 51000 Rijeka, Croatia University of Split – FESB, 21000 Split, Croatia University of Zagreb – FER, 10000 Zagreb Croatia University of Osijek, 31000 Osijek, Croatia Rudjer Boskovic Institute, 10000 Zagreb, Croatia
⁷ Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Salt Lake, Sector-1, Kolkata 700064, India
⁸ Max-Planck-Institut für Physik, 80805 München, Germany
⁹ Centro Brasileiro de Pesquisas Físicas (CBPF), 22290-180 URCA, Rio de Janeiro (RJ), Brasil
¹⁰ Unidad de Partículas y Cosmología (UPARCOS), Universidad Complutense, 28040 Madrid, Spain
¹¹ Inst. de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
¹² University of Łódź, Department of Astrophysics, 90236 Łódź, Poland
¹³ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹⁴ Institut de Física d’Altes Energies (IFAE), The Barcelona Institute of Science and Technology (BIST), 08193 Bellaterra (Barcelona), Spain
¹⁵ Università di Siena and INFN Pisa, 53100 Siena, Italy
¹⁶ Universität Würzburg, 97074 Würzburg, Germany
¹⁷ Finnish MAGIC Consortium: Tuorla Observatory (Department of Physics and Astronomy) and Finnish Centre of Astronomy with ESO (FINCA), University of Turku, 20014 Turku, Finland Astronomy Division, University of Oulu, 90014 Oulu, Finland
¹⁸ Departament de Física; CERES-IEEC, Universitat Autónoma de Barcelona, 08193 Bellaterra, Spain
¹⁹ Universitat de Barcelona, ICC, IEEC-UB, 08028 Barcelona, Spain
²⁰ Japanese MAGIC Consortium: ICRR, The University of Tokyo, 277-8582 Chiba, Japan Department of Physics, Kyoto University, 606-8502 Kyoto, Japan Tokai University, 259-1292 Kanagawa, Japan The University of Tokushima, 770-8502 Tokushima, Japan
²¹ Inst. for Nucl. Research and Nucl. Energy, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
²² Università di Pisa and INFN Pisa, 56126 Pisa, Italy
²³ Humboldt University of Berlin, Institut für Physik, 12489 Berlin, Germany
²⁴ Dipartimento di Fisica, Università di Trieste, 34127 Trieste, Italy
²⁵ Port d’Informació Científica (PIC), 08193 Bellaterra (Barcelona), Spain
²⁶ INAF-Trieste, Dept. of Physics & Astronomy, University of Bologna, Italy
²⁷ INFN, 35131 Padova, Italy
²⁸ ASI Science Data Center and INFN, 06123 Perugia, Italy
²⁹ CEN Bordeaux-Gradignan, 33170 Gradignan, France
³⁰ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
³¹ Instituto de Astrofísica de Andalucía (CSIC), Apartado 3004, 18080 Granada, Spain
³² Max–Planck–Institut für Radioastronomie, Auf dem Hügel, 69, 53121 Bonn, Germany
³³ Crimean Astrophysics Observatory, P/O Nauchny 298409, Crimea
³⁴ Astron. Inst., St. Petersburg State University, Russia
³⁵ Harvard-Smithsonian Center for Astrophysics, MA, 02138 Cambridge, USA
³⁶ Metsähovi Radio Observatory, Aalto University, 02540 Kylmälä, Finland
³⁷ Department of Electronics and Nanoengineering, Aalto University, 00076 Aalto, Finland
³⁸ Tuorla Observatory, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland
³⁹ Department of Physical Science, Hiroshima University, Higashihiroshima 739-8526, Japan
⁴⁰ Institute for Astrophysical Research, Boston University, Boston, MA 02215, USA
⁴¹ Mullard Space Science Lab., UCL, Dorking RH5 6NT, UK
⁴² Pulkovo Observatory, St.-Petersburg, Russia
⁴³ Kavli Institute for Particle Astrophysics and Cosmology, Stanford University and SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
⁴⁴ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
⁴⁵ Owens Valley Radio Observatory, California Institute of Technology, Pasadena, CA 91125, USA
⁴⁶ CePIA, Astronomy Department, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile
⁴⁷ Astrophysics Research Institute, Liverpool John Moores University, Brownlow Hill, Liverpool L3 5RF, UK

Received: 20 January 2018
Accepted: 30 June 2018

Abstract

Context. The BL Lac object S5 0716+714, a highly variable blazar, underwent an impressive outburst in January 2015 (Phase A), followed by minor activity in February (Phase B). The MAGIC observations were triggered by the optical flux observed in Phase A, corresponding to the brightest ever reported state of the source in the R-band.

Aims.The comprehensive dataset collected is investigated in order to shed light on the mechanism of the broadband emission.

Methods. Multi-wavelength light curves have been studied together with the broadband spectral energy distributions (SEDs). The sample includes data from Effelsberg, OVRO, Metsähovi, VLBI, CARMA, IRAM, SMA, Swift-UVOT, KVA, Tuorla, Steward, RINGO3, KANATA, AZT-8+ST7, Perkins, LX-200, Swift-XRT, NuSTAR, Fermi-LAT and MAGIC.

Results. The flaring state of Phase A was detected in all the energy bands, providing for the first time a multi-wavelength sample of simultaneous data from the radio band to the very-high-energy (VHE, E > 100 GeV). In the constructed SED, the Swift-XRT+NuSTAR data constrain the transition between the synchrotron and inverse Compton components very accurately, while the second peak is constrained from 0.1 GeV to 600 GeV by Fermi+MAGIC data. The broadband SED cannot be described with a one-zone synchrotron self-Compton model as it severely underestimates the optical flux in order to reproduce the X-ray to γ-ray data. Instead we use a two-zone model. The electric vector position angle (EVPA) shows an unprecedented fast rotation. An estimation of the redshift of the source by combined high-energy (HE, 0.1 GeV < E < 100 GeV) and VHE data provides a value of z = 0.31 ± 0.02_stats ± 0.05_sys, confirming the literature value.

Conclusions. The data show the VHE emission originating in the entrance and exit of a superluminal knot in and out of a recollimation shock in the inner jet. A shock–shock interaction in the jet seems responsible for the observed flares and EVPA swing. This scenario is also consistent with the SED modeling.