MAGIC long-term study of the distant TeV blazar PKS 1424+240 in a multiwavelength context^⋆

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 Technische Universität Dortmund, 44221 Dortmund, Germany
¹⁵ Inst. de Astrofísica de Andalucía (CSIC), 18080 Granada, Spain
¹⁶ Università di Padova and INFN, 35131 Padova, Italy
¹⁷ Università dell’Insubria, Como, 22100 Como, Italy
¹⁸ Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
¹⁹ Institut de Ciències de l’Espai (IEEC-CSIC), 08193 Bellaterra, Spain
²⁰ Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, 606-8501 Kyoto, Japan
²¹ Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, 900147 Oulu, Finland
²² Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
²³ Universitat de Barcelona, ICC, IEEC-UB, 08028 Barcelona, Spain
²⁴ Università di Pisa, and INFN Pisa, 56126 Pisa, Italy
²⁵ Now at: NASA Goddard Space Flight Center, Greenbelt MD 20771; and Department of Physics and Department of Astronomy, University of Maryland, College Park MD 20742, USA
²⁶ Now at: École polytechnique fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
²⁷ Now at: Department of Physics & Astronomy, UC Riverside, CA 92521, USA
²⁸ Finnish Centre for Astronomy with ESO (FINCA), Turku, Finland
²⁹ Also at: INAF via Tiepolo Giambattista, 34131 Trieste, Italy
³⁰ Also at Instituto de Fisica Teorica, UAM/CSIC, 28049 Madrid, Spain
³¹ Now at: Stockholm University, Oskar Klein Centre for Cosmoparticle Physics, 106 91 Stockholm, Sweden
³² Now at: GRAPPA Institute, University of Amsterdam, 1098 XH Amsterdam, The Netherlands
³³ Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA
³⁴ Cahill Center for Astronomy & Astrophysics, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, USA
³⁵ Department of Physics, Purdue University, 525 Northwestern Ave, West Lafayette, IN 47907, USA
³⁶ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
³⁷ AaltoUniversity, Department of Radio Science and Engineering, 02150 Espoo, Finland
³⁸ Department of Physics, University of Crete, Greece

Received: 1 January 2014
Accepted: 29 April 2014

Abstract

Aims. We present a study of the very high-energy (VHE; E> 100 GeV) γ-ray emission of the blazar PKS 1424+240 observed with the MAGIC telescopes. The primary aim of this paper is the multiwavelength spectral characterization and modeling of this blazar, which is made particularly interesting by the recent discovery of a lower limit of its redshift of z ≥ 0.6 and makes it a promising candidate to be the most distant VHE source.

Methods. The source has been observed with the MAGIC telescopes in VHE γ rays for a total observation time of ~33.6 h from 2009 to 2011. A detailed analysis of its γ-ray spectrum and time evolution has been carried out. Moreover, we have collected and analyzed simultaneous and quasi-simultaneous multiwavelength data.

Results. The source was marginally detected in VHE γ rays during 2009 and 2010, and later, the detection was confirmed during an optical outburst in 2011. The combined significance of the stacked sample is ~7.2σ. The differential spectra measured during the different campaigns can be described by steep power laws with the indices ranging from 3.5 ± 1.2 to 5.0 ± 1.7. The MAGIC spectra corrected for the absorption due to the extragalactic background light connect smoothly, within systematic errors, with the mean spectrum in 2009–2011 observed at lower energies by the Fermi-LAT. The absorption-corrected MAGIC spectrum is flat with no apparent turn down up to 400 GeV. The multiwavelength light curve shows increasing flux in radio and optical bands that could point to a common origin from the same region of the jet. The large separation between the two peaks of the constructed non-simultaneous spectral energy distribution also requires an extremely high Doppler factor if an one zone synchrotron self-Compton model is applied. We find that a two-component synchrotron self-Compton model describes the spectral energy distribution of the source well, if the source is located at z ~ 0.6.