The 2009 multiwavelength campaign on Mrk 421: variability and correlation studies

/ Authors

M. C. J. Aleksi'c, S. Ansoldi, L. A. Antonelli, P. Antoranz, A. Babić, P. Bangale, U. D. Almeida, J. Barrio, J. Gonz'alez, W. Bednarek

and 490 more authors

K. Berger, E. Bernardini, A. Biland, O. Blanch, R. Bock, S. Bonnefoy, G. Bonnoli, F. Borracci, T. Bretz, E. Carmona, A. Carosi, D. Fidalgo, P. Colin, E. Colombo, J. Contreras, J. Cortina, S. Covino, P. D. Vela, F. Dazzi, A. Angelis, G. Caneva, B. Lotto, C. Mendez, M. Doert, A. Domínguez, D. Prester, D. Dorner, M. Doro, S. Einecke, D. Eisenacher, D. Elsaesser, E. Farina, D. Ferenc, M. Fonseca, L. Font, K. Frantzen, C. Fruck, R. L'opez, M. Garczarczyk, D. G. Terrats, M. Gaug, G. Giavitto, N. Godinovi'c, A. M. noz, S. Gozzini, A. Hadamek, D. Hadasch, A. Herrero, D. Hildebrand, J. Hose, D. Hrupec, W. Idec, V. Kadenius, H. Kellermann, M. Knoetig, J. Krause, J. Kushida, A. Barbera, D. Lelas, N. Lewandowska, E. Lindfors, F. Longo, S. Lombardi, M. L'opez, R. L'opez-Coto, A. L'opez-Oramas, E. Lorenz, I. Lozano, M. Makariev, K. Mallot, G. Maneva, N. Mankuzhiyil, K. Mannheim, L. Maraschi, B. Marcote, M. Mariotti, M. Mart'inez, D. Mazin, U. Menzel, M. Meucci, J. Miranda, R. Mirzoyan, A. Moralejo, P. Munar-Adrover, D. Nakajima, A. Niedźwiecki, K. Nilsson, N. Nowak, R. Orito, A. Overkemping, S. Paiano, M. Palatiello, D. Paneque, R. Paoletti, J. Paredes, X. Paredes-Fortuny, S. Partini, M. Persic, F. Prada, P. Moroni, E. Prandini, S. Preziuso, I. Puljak, R. Reinthal, W. Rhode, M. Rib'o, J. Rico, J. Garcia, S. Rugamer, A. Saggion, K. Saito, M. Salvati, K. Satalecka, V. Scalzotto, V. Scapin, C. Schultz, T. Schweizer, S. Shore, A. Sillanpaa, J. Sitarek, I. Šnidarić, D. Sobczynska, F. Spanier, V. Stamatescu, A. Stamerra, T. Steinbring, J. Storz, S. Sun, T. Suri'c, L. Takalo, F. Tavecchio, P. Temnikov, T. Terzi'c, D. Tescaro, M. Teshima, J. Thaele, O. Tibolla, D. Torres, T. Toyama, A. Treves, M. Uellenbeck, P. Vogler, R. Wagner, F. Zandanel, R. Zanin, V. C. S. Archambault, B. Behera, M. Beilicke, W. Benbow, R. Bird, J. Buckley, V. Bugaev, M. Cerruti, X. Chen, L. Ciupik, E. Collins-Hughes, W. Cui, J. Dumm, J. Eisch, A. Falcone, S. Federici, Q. Feng, J. Finley, H. Fleischhack, P. Fortin, L. Fortson, A. Furniss, S. Griffin, S. Griffiths, J. Grube, G. Gyuk, D. Hanna, J. Holder, G. Hughes, T. Humensky, C. Johnson, P. Kaaret, M. Kertzman, Y. Khassen, D. Kieda, H. Krawczynski, F. Krennrich, S. Kumar, M. Lang, G. Maier, S. McArthur, K. Meagher, P. Moriarty, R. Mukherjee, R. Ong, A. Otte, N. Park, A. Pichel, M. Pohl, A. Popkow, H. Prokoph, J. Quinn, K. Ragan, J. Rajotte, P. Reynolds, G. Richards, E. Roache, A. Rovero, G. Sembroski, K. Shahinyan, D. Staszak, I. Telezhinsky, M. Theiling, J. Tucci, J. Tyler, A. Varlotta, S. Wakely, T. Weekes, A. Weinstein, R. Welsing, A. Wilhelm, D. Williams, B. Zitzer, E. C. M. Villata, C. Raiteri, H. Aller, M. Aller, W. P. Chen, B. Jordan, E. Koptelova, O. Kurtanidze, A. Lahteenmaki, B. Mcbreen, V. Larionov, C. Lin, M. Nikolashvili, E. Angelakis, M. Capalbi, A. C. nana, L. Carrasco, P. Cassaro, A. Cesarini, L. Fuhrmann, M. Giroletti, T. Hovatta, T. Krichbaum, H. Krimm, W. Max-Moerbeck, J. Moody, G. Maccaferri, Y. Mori, I. Nestoras, A. Orlati, C. Pace, R. Pearson, M. Perri, A. Readhead, J. Richards, A. Sadun, T. Sakamoto, J. Tammi, M. Tornikoski, Y. Yatsu, A. Z. Ifae, Edifici Cn., Campus Uab, E-08193 Bellaterra, Spain., U. Udine, I. Trieste, I. Udine, Italy., I. I. F. Astrophysics, I. Rome, U. Siena, I. Pisa, I-53100 Siena, Croatian Magic Consortium, Rudjer Boskovic Institute, University of Rijeka, University of Split, HR-10000 Zagreb, Croatia., M. F. Physik, D-80805 Munchen, H Germany, U. Complutense, E. Madrid, Instituto de Astrof'isica de Canarias, E. Laguna, Tenerife, U. Lodz, PL-90236 Lodz, Poland, D. Elektronen-Synchrotron, D. Zeuthen, E. Zurich, CH-8093 Zurich, Switzerland., U. Wurzburg, D-97074 Wurzburg, Centro de Investigaciones Energ'eticas, Medioambientales y Tecnol'ogicas, Technische Universitat Dortmund, D. Dortmund, Inst. de Astrof'isica de Andaluc'ia, E-18080 Granada, U. Padova, Infn, I-35131 Padova, U. dell'Insubria, Como, I-22100 Como, Unitat de F'isica de les Radiacions, Departament de F'isica, CERES-IEEC, U. Barcelona, Institut de Ci'encies de l'Espai, Finnish Magic Consortium, T. Observatory, U. Turku, D. Physics, U. Oulu, Finland., Japanese Magic Consortium, D. Physics, Astronomy, Kyoto University, Japan., Inst. for Nucl. Research, Nucl. Energy, BG-1784 Sofia, Bulgaria., U. Barcelona, Es Barcelona, U. Pisa, I. Pisa, N. C. E. P. F. D. Lausanne, Lausanne, now at Department of Physics Astronomy, U. Riverside, CA 92521, Usa, N. Eso, Turku, also at INAF-Trieste, A. M. D. D. F. Teorica, Uamcsic, E. Madrid, now at Stockholm University, Fysikum, Oskar Klein Centre, Albanova, S. Stockholm, Sweden., Now at Grappa Institute, U. Amsterdam, 1098XH Amsterdam, Netherlands., D. O. Astronomy, P. Department, M. University, Montreal, QC H3A 2T8, Canada., Desy, 6. Platanenallee, 15738 Zeuthen, W. University, S. Louis, MO 63130, Fred Lawrence Whipple Observatory, H. C. F. Astrophysics, Amado, AZ 85645, S. O. Physics, University College Dublin, Belfield, 4. Dublin, Ireland, I. O. Physics, U. Potsdam, 14476 Potsdam-Golm, A. Department, Adler Planetarium, Astronomy Museum, Chicago., IL 60605, Purdue University, W. Lafayette, IN 47907, U. Minnesota, Minneapolis, MN 55455, I. S. University, Ames, IA 50011, Astrophysics, 525 Davey Lab, P. S. University, University Park, Pa 16802, Santa Cruz Institute for Particle Physics, U. California, Santa Cruz, CA 95064, U. Iowa, Van Allen Hall, Iowa City, IA 52242, T. B. R. Institute, U. Delaware, Newark, DE 19716, Columbia University, New York., NY 10027, D. University, Greencastle, IN 46135-0037, U. Utah, Salt lake City, UT 84112, National University of Ireland Galway, University Road, Galway., Enrico Fermi Institute, U. Chicago, IL 60637, Center for Computational Astrophysics, G. I. O. Technology, NW 837StateStreet, Atlanta, GA 30332-0430, D. Life, P. Sciences, Galway-Mayo Institute of Technology, Dublin Road, Barnard College, L. Angeles, CA 90095, Instituto de Astronomia y Fisica del Espacio, 28 CasilladeCorreo67-Sucursal, Ciudad de Buenos Aires, Argentina., D. Physics, Instrumentation, Cork Institute of Technology, Bishopstown, Cork, A. N. Laboratory, 9. S. C. Avenue, Argonne, IL 60439, Cambridge, MA 02138, -INAF, Osservatorio astronomico di Torino, I. P. Torinese, U. Michigan, A. Arbor, MI 48109-1042, G. I. O. Astronomy, National Central University, Jhongli 32054, Taiwan, S. O. Physics, Dublin Institute for Advanced Studies, Dublin., M. University, Sternberg Astronomical Institute, Russia., A. Observatory, Mt. Kanobili, 0301 Abastumani, Georgia, Landessternwarte, Zentrum fur Astronomie der Universitat Heidelberg, 17 Konigstuhl, 69117 Heidelberg, A. Finland, Aalto University Department of Radio Science, Engineering, P. 13000, FI-00076 Aalto, Isaac Newton Institute of Chile, St.-Petersburg Branch, S. Petersburg, P. Observatory, 196140 St. Petersburg, A. Institute, S. University, M. F. Radioastronomie, 69 AufdemHugel, 53121 Bonn

/ Abstract

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.

Journal: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/201424216