Long-term multi-wavelength variability and correlation study of Markarian 421 from 2007 to 2009

We study the multi-band variability and correlations of the TeV blazar Mrk 421 on year time scales, which can bring additional insight on the processes responsible for its broadband emission. We observed Mrk 421 in the very high energy (VHE) gamma-ray range with the Cherenkov telescope MAGIC-I from March 2007 to June 2009 for a total of 96 hours of effective time after quality cuts. The VHE flux variability is quantified with several methods, including the Bayesian Block algorithm, which is applied to data from Cherenkov telescopes for the first time. The 2.3 year long MAGIC light curve is complemented with data from the Swift/BAT and RXTE/ASM satellites and the KVA, GASP-WEBT, OVRO, and Metsahovi telescopes from February 2007 to July 2009, allowing for an excellent characterisation of the multi-band variability and correlations over year time scales. Mrk 421 was found in different gamma-ray emission states during the 2.3 year long observation period. Flares and different levels of variability in the gamma-ray light curve could be identified with the Bayesian Block algorithm. The same behaviour of a quiet and active emission was found in the X-ray light curves measured by Swift/BAT and the RXTE/ASM, with a direct correlation in time. The behaviour of the optical light curve of GASP-WEBT and the radio light curves by OVRO and Metsahovi are different as they show no coincident features with the higher energetic light curves and a less variable emission. The fractional variability is overall increasing with energy. The comparable variability in the X-ray and VHE bands and their direct correlation during both high- and low-activity periods spanning many months show that the electron populations radiating the X-ray and gamma-ray photons are either the same, as expected in the Synchrotron-Self-Compton mechanism, or at least strongly correlated, as expected in electromagnetic cascades.

Engineering | India. | Dublin Institute for Advanced Studies | Ireland | L. A. Antonelli | Taiwan | Tenerife | Greenbelt | Lausanne | Technology | W. P. Chen | University College Dublin | M. V. Fonseca | Denver | Technische Universitat Dortmund | H Germany | D. O. Astronomy | Usa | E. Madrid | Spain. | Instituto de Astrof'isica de Canarias | U. L. Laguna | Brazil. | M. F. Physik | 1290 | Versoix | Switzerland. | D. D. F'isica | Finland. | I-35131 Padova | Italy. | T. U. O. Tokyo | Japan. | S. O. Physics | U. Barcelona | U. Padova | Georgia | K. Nishijima | E. Bernardini | W. Rhode | K. Satalecka | U. Maryland | Russia. | College Park | S. Ansoldi | O. Blanch | R. Paoletti | I. Torino | U. Colorado | A. Angelis | B. Lotto | D. Lelas | I. Puljak | K. Mannheim | Kyoto University | Infn | A. Treves | K. Noda | A. Biland | R. Mirzoyan | M. Teshima | M. V. E. Zurich | V. Neustroev | D. Paneque | M. Will | T. Toyama | N. Efimova | T. Saito | J. Poutanen | T. Schweizer | E. Koptelova | D. Blinov | T. Hovatta | C. Raiteri | V. Larionov | S. Covino | Campus Uab | D. Elektronen-Synchrotron | F. Longo | Kek | S. Shore | Inst. for Nucl. Research | M. Makariev | V. Verguilov | H. Kubo | Institut de F'isica d'Altes Energies | C. Fruck | P. Majumdar | Poland | M. Gaug | L. Maraschi | J. Kushida | J. Ward | M. Mariotti | D. Góra | S. Paiano | K. Frantzen | H. Center | U. Crete | D. Guberman | F. Dazzi | M. Wu | P. Antoranz | A. Babić | J. Barrio | W. Bednarek | G. Bonnoli | S. Buson | A. Carosi | P. Colin | J. Contreras | J. Cortina | E. O. Wilhelmi | F. Pierro | D. Dorner | M. Doro | S. Einecke | L. Font | A. G. Muñoz | D. Hadasch | M. Hayashida | D. Hrupec | K. Kodani | Y. Konno | E. Lindfors | G. Maneva | D. Mazin | J. Miranda | D. Nakajima | A. Niedźwiecki | R. Orito | J. Paredes | G. Pedaletti | M. Persic | E. Prandini | J. Rico | C. Schultz | J. Sitarek | D. Sobczynska | A. Stamerra | L. Takalo | H. Takami | P. Temnikov | M. Tornikoski | D. Torres | R. Zanin | E. Moretti | F. Tavecchio | B. Mcbreen | B. Jordan | I. Trieste | P. Bangale | U. D. Almeida | J. Gonz'alez | S. Bonnefoy | F. Borracci | E. Colombo | P. D. Vela | D. D. Prester | D. Elsaesser | R. L'opez | M. Garczarczyk | D. G. Terrats | N. Godinovi'c | J. Herrera | J. Hose | W. Idec | A. Barbera | S. Lombardi | M. L'opez | R. L'opez-Coto | K. Mallot | B. Marcote | M. Mart'inez | U. Menzel | A. Moralejo | K. Nilsson | A. Overkemping | M. Palatiello | X. Paredes-Fortuny | P. Moroni | M. Rib'o | A. Sillanpaa | I. Šnidarić | T. Steinbring | M. Strzys | T. Terzi'c | D. Tescaro | J. Thaele | E-08193 Bellaterra | U. Udine | I. Udine | I. I. F. Astrophysics | I. Rome | U. Siena | I. Pisa | I. Siena | Croatian Magic Consortium | Rudjer Boskovic Institute | University of Rijeka | University of Split | Croatia. | D-80805 Munchen | U. Complutense | E-38200 La Laguna | D. Zeuthen | CH-8093 Zurich | U. Wurzburg | D-97074 Wurzburg | D. Dortmund | Unitat de F'isica de les Radiacions | CERES-IEEC | Japanese Magic Consortium | Finnish Magic Consortium | T. Observatory | U. Turku | U. Oulu | Nucl. Energy | BG-1784 Sofia | Bulgaria. | Icc | IEEC-UB | E. Barcelona | U. Pisa | now at Nasa Goddard Space Flight Center | MD 20771 | MD 20742 | N. C. E. P. F. D. Lausanne | N. Eso | Turku | also at INAF-Trieste | Greece. | Heraklion | D. Glawion | A. Sadun | T. Science | Icrea | L. Perri | Y. Hanabata | University of L'od'z | R. Clavero | O. Kurtanidze | S. O. Kurtanidze | M. Nikolashvili | I. Vovk | A. Hahn | M. Manganaro | P. Giammaria | B. Biasuzzi | A. Fern'andez-Barral | D. Fidalgo | D. Galindo | Belfield | M. N. Rosillo | Kazan Federal University | T. Grishina | E. Kopatskaya | L. Larionova | D. Morozova | Metsahovintie 114 | S. Univ. | St.-Petersburg | National Central University | Mt. Kanobili | 0301 Abastumani | Tatarstan | M. L. Ahnen | B. Banerjee | A. Chatterjee | J. Palacio | U. Zagreb | Saha Institute of Nuclear Physics | Institute for Space Sciences | Icrr | T. University | The University of Tokushima | Now at Centro Brasileiro de Pesquisas F'isicas | H. Berlin | also at Japanese Magic Consortium | A. T. C. F. Astrophysics | G. Kimeridze | R. Ligustri | J. A. Ros | L. Sigua | University of Zagreb | L. Nogu'es | T. Bretz | E. Larionova | I. Troitsky | 1. Bidhannagar | Salt Lake | Sector-1 | Kolkata 700064 | D. Astrof'isica | A. Division | P. Observatory | A. Observatory | E. A. Observatory | G. I. O. Astronomy | A. L. M. R. Observatory | R. Sigaud | 4. Dublin | 08193 Bellaterra | 150 - Urca | RJ RiodeJaneiro- | 22290-180 | P. 13000 | FI-00076 Aalto | Astron. Inst. | FI-02540 Kylmala | Circolo Astrofili Talmassons | Agrupaci'o Astronomica de Sabadell | 15 InstitutfurPhysikNewtonstr. | 12489 Berlin Germany | D. Physics | Aalto University Department of Radio Science | G. Hughes | A. Domínguez | Tao-yuan | PL-90236 Lodz | H. C. Lin | L. Antonelli | J. R. Garcia | E. Forn'e | A. Lahteenmaaki | 300 Zhongda Rd | Zhongli 32001 | 1. P. Torinese | M. H. Wu | J. R. Garcia | J. Ward | E. Wilhelmi | A. M. C. F. Astrophysics | E. Bernardini | Usa | I. Puljak | T. Saito | J. Garcia | F. D. Pierro | T. Z. F. O. Science

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