Insights into the emission of the blazar 1ES 1011+496 through unprecedented broadband observations during 2011 and 2012

¹ IFAE, Campus UAB, 08193 Bellaterra, Spain
² Università di Udine, and INFN Trieste, 33100 Udine, Italy
³ INAF National Institute for Astrophysics, 00136 Rome, Italy
⁴ Università di Siena, and INFN Pisa, 53100 Siena, Italy
⁵ Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, 10000 Zagreb, Croatia
⁶ Max-Planck-Institut für Physik, 80805 München, Germany
⁷ Universidad Complutense, 28040 Madrid, Spain
⁸ Inst. de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
⁹ University of Łódź, 90236 Lodz, Poland
¹⁰ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹¹ ETH Zurich, 8093 Zurich, Switzerland
¹² Universität Würzburg, 97074 Würzburg, Germany
¹³ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, 28040 Madrid, Spain
¹⁴ Institute of Space Sciences, 08193 Barcelona, Spain
¹⁵ Università di Padova and INFN, 35131 Padova, Italy
¹⁶ Technische Universität Dortmund, 44221 Dortmund, Germany
¹⁷ Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
¹⁸ Universitat de Barcelona, ICC, IEEC-UB, 08028 Barcelona, Spain
¹⁹ Japanese MAGIC Consortium, KEK, Department of Physics and Hakubi Center, Kyoto University, Tokai University, The University of Tokushima, ICRR, The University of Tokyo, Tokyo, Japan
²⁰ Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Oulu, Finland
²¹ Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
²² Università di Pisa, and INFN Pisa, 56126 Pisa, Italy
²³ ICREA and Institute of Space Sciences, 08193 Barcelona, Spain
²⁴ Università dell’Insubria and INFN Milano Bicocca, Como, 22100 Como, Italy
²⁵ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA and Department of Physics and Department of Astronomy, University of Maryland, College Park, MD 20742, USA
²⁶ École polytechnique fédérale de Lausanne (EPFL), 1290 Lausanne, Switzerland
²⁷ Institut für Astro- und Teilchenphysik, Leopold-Franzens- Universität Innsbruck, 6020 Innsbruck, Austria
²⁸ Finnish Centre for Astronomy with ESO (FINCA), Turku, Finland
²⁹ INAF-Trieste, Italy
³⁰ ISDC – Science Data Center for Astrophysics, 1290 Versoix Geneva, Switzerland
³¹ Centro Brasileiro de Pesquisas Físicas (CBPF/MCTI), R. Dr. Xavier Sigaud, 150 – Urca, Rio de Janeiro – RJ, 22290-180, Brazil
³² INAF-IRA Bologna, via Gobetti 101, 40129 Bologna, Italy
³³ Aalto University Metsähovi Radio Observatory Kylmälä, Finland
³⁴ Aalto University Dept of Radio Science and Engineering, Espoo, Finland
³⁵ Cahill Center of Astronomy and Astrophysics, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, USA
³⁶ Astro Space Center of Lebedev Physical Institute, Profsoyuznaya 84/32, 117997 Moscow, Russia
³⁷ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³⁸ Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907, USA
³⁹ NationalRadio Astronomy Observatory, PO Box 0, Socorro, NM 87801, USA
⁴⁰ Astrophysics Research Institute, Liverpool John Moore University, UK
⁴¹ Pulkovo Observatory, Pulkovskoe Chaussee 65/1, 196140 St. Petersburg, Russia
⁴² Crimean Astrophysical Observatory, 98409 Nauchny, Crimea, Ukraine
⁴³ Laboratoire d’Annecy-le-Vieux de Physique des Particules, Université Savoie Mont-Blanc, CNRS/IN2P3, 74941 Annecy-le-Vieux, France

^⋆ Coresponding authors: C. Arcaro, e-mail: cornelia.arcaro@pd.infn.it; U. Barres de Almeida, e-mail: ulisses@cbpf.br; S. Paiano, e-mail: simona.paiano@pd.infn.it

Received: 12 August 2015
Accepted: 10 February 2016

Abstract

Context. 1ES 1011+496 (z = 0.212) was discovered in very high-energy (VHE, E> 100 GeV) γ rays with MAGIC in 2007. The absence of simultaneous data at lower energies led to an incomplete characterization of the broadband spectral energy distribution (SED).

Aims. We study the source properties and the emission mechanisms, probing whether a simple one-zone synchrotron self-Compton (SSC) scenario is able to explain the observed broadband spectrum.

Methods. We analyzed data in the range from VHE to radio data from 2011 and 2012 collected by MAGIC, Fermi-LAT, Swift, KVA, OVRO, and Metsähovi in addition to optical polarimetry data and radio maps from the Liverpool Telescope and MOJAVE.

Results. The VHE spectrum was fit with a simple power law with a photon index of 3.69 ± 0.22 and a flux above 150 GeV of (1.46 ± 0.16) × 10^-11 ph cm^-2 s^-1. The source 1ES 1011+496 was found to be in a generally quiescent state at all observed wavelengths, showing only moderate variability from radio to X-rays. A low degree of polarization of less than 10% was measured in optical, while some bright features polarized up to 60% were observed in the radio jet. A similar trend in the rotation of the electric vector position angle was found in optical and radio. The radio maps indicated a superluminal motion of 1.8 ± 0.4 c, which is the highest speed statistically significant measured so far in a high-frequency-peaked BL Lac.

Conclusions. For the first time, the high-energy bump in the broadband SED of 1ES 1011+496 could be fully characterized from 0.1 GeV to 1 TeV, which permitted a more reliable interpretation within the one-zone SSC scenario. The polarimetry data suggest that at least part of the optical emission has its origin in some of the bright radio features, while the low polarization in optical might be due to the contribution of parts of the radio jet with different orientations of the magnetic field with respect to the optical emission.