Issue |
A&A
Volume 576, April 2015
|
|
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Article Number | A126 | |
Number of page(s) | 18 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201424216 | |
Published online | 17 April 2015 |
The 2009 multiwavelength campaign on Mrk 421: Variability and correlation studies⋆,⋆⋆
1 IFAE, Edifici Cn., 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 Lodz, 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 Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, 900147 Oulu, Finland
21 Japanese MAGIC Consortium, Division of Physics and Astronomy, 606-8501 Kyoto University, Japan
22 Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
23 Universitat de Barcelona (ICC/IEEC), 08028 Barcelona, Spain
24 Università di Pisa, and INFN Pisa, 56126 Pisa, Italy
25 Now at École polytechnique fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
26 Now at Department of Physics & Astronomy, UC Riverside, CA 92521, USA
27 Now at Finnish Centre for Astronomy with ESO (FINCA), Turku, 21500 Piikkiö, Finland
28 Now at Stockholm University, Fysikum, Oskar Klein Centre, AlbaNova, 106 91 Stockholm, Sweden
29 Now at GRAPPA Institute, University of Amsterdam, 1098 XH Amsterdam, Netherlands
30 Now at Stockholm University, Department of Astronomy, Oskar Klein Centre, AlbaNova, 106 91 Stockholm, Sweden
31 Physics Department, McGill University, Montreal, QC H3A 2T8, Canada
32 DESY, Platanenallee 6, 15738 Zeuthen, Germany
33 Department of Physics, Washington University, St. Louis, MO 63130, USA
34 Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA
35 School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
36 Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany
37 Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA
38 Department of Physics andAstronomy, Purdue University, West Lafayette, IN 47907, USA
39 School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA
40 Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA
41 Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA
42 Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA
43 Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA
44 Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA
45 Physics Department, Columbia University, New York, NY 10027, USA
46 Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA
47 Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA
48 School of Physics, National University of Ireland Galway, University Road, Galway, Ireland
49 Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA
50 School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430, USA
51 Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland
52 Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027, USA
53 Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
54 Instituto de Astronomia y Fisica del Espacio, Casilla de Correo 67 – Sucursal 28, (C1428ZAA) Ciudad Autonoma de Buenos Aires, 1428 Buenos Aires, Argentina
55 Department of Applied Physics and Instrumentation, Cork Institute of Technology, Bishopstown, Cork, Ireland
56 Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA
57 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
58 INAF–Osservatorio Astronomico di Torino, 10025 Pino Torinese (TO), Italy
59 Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042, USA
60 Graduate Institute of Astronomy, National Central University, Jhongli 32054, Taiwan
61 School of Cosmic Physics, Dublin Institute for Advanced Studies, Dublin, 2, Ireland
62 Moscow M.V. Lomonosov State University, Sternberg Astronomical Institute, 119992 Moscow, Russia
63 Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia
64 Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
65 Aalto University Metsähovi Radio Observatory Metsähovintie 114 02540 Kylmälä, Finland
66 Aalto University Department of Radio Science and Engineering, PO Box 13000, 00076 Aalto, Finland
67 University College Dublin, Belfield, Dublin 4, Ireland
68 Isaac Newton Institute of Chile, St. Petersburg Branch, 196140 St. Petersburg, Russia
69 Pulkovo Observatory, 196140 St. Petersburg, Russia
70 Astronomical Institute, St. Petersburg State University, 198504 St. Petersburg, Russia
71 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
72 Instituto Nacional de Astrofísica, Óptica y Electrónica, Tonantzintla, Puebla 72840, Mexico
73 INAF Istituto di Radioastronomia, Sezione di Noto, Contrada Renna Bassa, 96017 Noto (SR), Italy
74 Department of Physics, University of Trento, 38050 Povo, Trento, Italy
75 Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, USA
76 Astro Space Center of the Lebedev Physical Institute, 117997 Moscow, Russia
77 Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
78 Indiana University, Department of Astronomy, Swain Hall West 319, Bloomington, IN 47405-7105, USA
79 Department of Physics and Astronomy, Brigham Young University, Provo, UT 84602, USA
80 INAF Istituto di Radioastronomia, Stazione Radioastronomica di Medicina, 40059 Medicina (Bologna), Italy
81 Department of Physics, Tokyo Institute of Technology, Meguro City, Tokyo 152-8551, Japan
82 ASI-Science Data Center, via del Politecnico, 00133 Rome, Italy
83 Department of Physics, Purdue University, 525 Northwestern Ave, West Lafayette, IN 47907, USA
84 Department of Physics, University of Colorado, Denver, CO 80220, USA
85 Department of Physics and Mathematics, College of Science and 952 Engineering, Aoyama Gakuin University, 5-10-1 Fuchinobe, Chuoku, Sagamihara-shi Kanagawa 252-5258, Japan
86 Department of Physics and Astronomy, Pomona College, Claremont CA 91711-6312, USA
87 INAF Istituto di Radioastronomia, 40129 Bologna, Italy
Received: 15 May 2014
Accepted: 16 January 2015
Aims. We perform an extensive characterization of the broadband emission of Mrk 421, as well as its temporal evolution, during the non-flaring (low) state. The high brightness and nearby location (z = 0.031) of Mrk 421 make it an excellent laboratory to study blazar emission. The goal is to learn about the physical processes responsible for the typical emission of Mrk 421, which might also be extended to other blazars that are located farther away and hence are more difficult to study.
Methods. We performed a 4.5-month multi-instrument campaign on Mrk 421 between January 2009 and June 2009, which included VLBA, F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other instruments and collaborations. This extensive radio to very-high-energy (VHE; E> 100 GeV) γ-ray dataset provides excellent temporal and energy coverage, which allows detailed studies of the evolution of the broadband spectral energy distribution.
Results. Mrk421 was found in its typical (non-flaring) activity state, with a VHE flux of about half that of the Crab Nebula, yet the light curves show significant variability at all wavelengths, the highest variability being in the X-rays. We determined the power spectral densities (PSD) at most wavelengths and found that all PSDs can be described by power-laws without a break, and with indices consistent with pink/red-noise behavior. We observed a harder-when-brighter behavior in the X-ray spectra and measured a positive correlation between VHE and X-ray fluxes with zero time lag. Such characteristics have been reported many times during flaring activity, but here they are reported for the first time in the non-flaring state. We also observed an overall anti-correlation between optical/UV and X-rays extending over the duration of the campaign.
Conclusions. The harder-when-brighter behavior in the X-ray spectra and the measured positive X-ray/VHE correlation during the 2009 multi-wavelength campaign suggests that the physical processes dominating the emission during non-flaring states have similarities with those occurring during flaring activity. In particular, this observation supports leptonic scenarios as being responsible for the emission of Mrk 421 during non-flaring activity. Such a temporally extended X-ray/VHE correlation is not driven by any single flaring event, and hence is difficult to explain within the standard hadronic scenarios. The highest variability is observed in the X-ray band, which, within the one-zone synchrotron self-Compton scenario, indicates that the electron energy distribution is most variable at the highest energies.
Key words: BL Lacertae objects: individual: Mrk 421
Appendix A is available in electronic form at http://www.aanda.org
The complete data set shown in Fig. 1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/576/A126
© ESO, 2015
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