MAGIC gamma-ray and multi-frequency observations of flat spectrum radio quasar PKS 1510−089 in early 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 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, 606-8901 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 Ecole polytechnique fédérale de Lausanne (EPFL), 105 Lausanne, Switzerland
²⁷ now at Department of Physics & Astronomy, UC Riverside CA 92521, USA
²⁸ now at Finnish Centre for Astronomy with ESO (FINCA), 21500 Piikkiö, Turku, Finland
²⁹ also at INAF-Trieste, 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, 1098XH Amsterdam, The Netherlands
³³ Dipartimento di Fisica, Università degli Studi di Perugia, via A. Pascoli, 06123 Perugia; INFN Sezione di Perugia, via A. Pascoli, 06123 Perugia, Italy
³⁴ ASI Science Data Centre (ASDC), via del Politecnico snc, 00133 Roma, INAF-OAR, via Frascati 33, 00040 Monte Porzio Catone ( RM), Italy
³⁵ INAF-IASF Palermo, via Ugo La Malfa 153, 90146 Palermo, Italy
³⁶ Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD, UK
³⁷ Tuorla Observatory, Department of Physics and Astronomy, University of Turku, 21500 Piikkiö, Finland
³⁸ INAF – Osservatorio Astrofisico di Torino, 10025 Pino Torinese Torino, Italy
³⁹ Aalto University Metsähovi Radio Observatory, Metsähovintie 114, 02540 Kylmälä, Finland
⁴⁰ Aalto University Department of Radio Science and Engineering, 02150 Espoo, Finland
⁴¹ Cahill Center for Astronomy & Astrophysics, Caltech, 1200 E. California Blvd, Pasadena CA 91125, USA
⁴² Department of Physics, Purdue University, 525 Northwestern Ave, West Lafayette IN 47907, USA
⁴³ Institute for Astrophysical Research, Boston University, USA
⁴⁴ INAF-IRA Bologna, Italy
⁴⁵ Harvard-Smithsonian Center for Astrophysics, Cambridge MA 02138, USA
⁴⁶ Astron. Inst., St.-Petersburg State Univ., Russia
⁴⁷ Pulkovo Observatory, St.-Petersburg, Russia
⁴⁸ Isaac Newton Institute of Chile, St.-Petersburg Branch, Russia
⁴⁹ University of Crete, Heraklion, Greece
⁵⁰ Graduate Institute of Astronomy, National Central University, 300 Jhongda Rd., Jhongli 32001, Taiwan
⁵¹ Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁵² Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18080 Granada, Spain
⁵³ Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia
⁵⁴ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁵⁵ Engelhardt Astronomical Observatory, Kazan Federal University, 422526 Tatarstan, Russia
⁵⁶ Instituto de Astrofisica de Canarias (IAC), 38205 San Critóbal, La Laguna, Tenerife, Spain
⁵⁷ Departamento de Astrofisica, Universidad de La Laguna, 38206 , La Laguna, Tenerife, Spain
⁵⁸ Sofia University, 1000 Sofia, Bulgaria
⁵⁹ Department of Astronomy, University of Michigan, 817 Dennison Bldg., Ann Arbor MI 48109-1042, USA
⁶⁰ Max-Planck-Institut für Radioastronomie, Auf dem Huegel 69, 53121 Bonn, Germany
⁶¹ Institut de Radio Astronomie Millimétrique, Avenida Divina Pastora 7, Local 20, 18012 Granada, Spain
⁶² Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, 252-5210 Kanagawa, Japan
⁶³ Astronomical Observatory, Jagiellonian University, 30-244 Krakow, Poland

Received: 22 January 2014
Accepted: 30 May 2014

Abstract

Aims. Amongst more than fifty blazars detected in very high energy (VHE, E> 100 GeV) γ rays, only three belong to the subclass of flat spectrum radio quasars (FSRQs). The detection of FSRQs in the VHE range is challenging, mainly because of their soft spectra in the GeV-TeV regime. MAGIC observed PKS 1510−089 (z = 0.36) starting 2012 February 3 until April 3 during a high activity state in the high energy (HE, E> 100 MeV) γ-ray band observed by AGILE and Fermi. MAGIC observations result in the detection of a source with significance of 6.0 standard deviations (σ). We study the multi-frequency behaviour of the source at the epoch of MAGIC observation, collecting quasi-simultaneous data at radio and optical (GASP-WEBT and F-Gamma collaborations, REM, Steward, Perkins, Liverpool, OVRO, and VLBA telescopes), X-ray (Swift satellite), and HE γ-ray frequencies.

Methods. We study the VHE γ-ray emission, together with the multi-frequency light curves, 43 GHz radio maps, and spectral energy distribution (SED) of the source. The quasi-simultaneous multi-frequency SED from the millimetre radio band to VHE γ rays is modelled with a one-zone inverse Compton model. We study two different origins of the seed photons for the inverse Compton scattering, namely the infrared torus and a slow sheath surrounding the jet around the Very Long Baseline Array (VLBA) core.

Results. We find that the VHE γ-ray emission detected from PKS 1510−089 in 2012 February-April agrees with the previous VHE observations of the source from 2009 March-April. We find no statistically significant variability during the MAGIC observations on daily, weekly, or monthly time scales, while the other two known VHE FSRQs (3C 279 and PKS 1222+216) have shown daily scale to sub-hour variability. The γ-ray SED combining AGILE, Fermi and MAGIC data joins smoothly and shows no hint of a break. The multi-frequency light curves suggest a common origin for the millimetre radio and HE γ-ray emission, and the HE γ-ray flaring starts when the new component is ejected from the 43 GHz VLBA core and the studied SED models fit the data well. However, the fast HE γ-ray variability requires that within the modelled large emitting region, more compact regions must exist. We suggest that these observed signatures would be most naturally explained by a turbulent plasma flowing at a relativistic speed down the jet and crossing a standing conical shock.