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

• Published in: arXiv.org 2015-02
• Main Authors: Antoranz, P, Babic, A, Barrio, J A, J Becerra González, Bernardini, E, Blanch, O, Bock, R K, Carmona, E, Carosi, A, Colin, P, Contreras, J L, De Angelis, A, C Delgado Mendez, Domínguez, A, D Dominis Prester, Dorner, D, Doro, M, Eisenacher, D, Elsaesser, D, Farina, E, Font, L, D Garrido Terrats, Giavitto, G, Godinović, N, Gozzini, S R, Hadasch, D, Herrero, A, Hildebrand, D, Hose, J, Kellermann, H, Krause, J, Lelas, D, Lewandowska, N, Lombardi, S, López-Coto, R, Lorenz, E, Makariev, M, Mankuzhiyil, N, Maraschi, L, Mariotti, M, Martínez, M, Meucci, M, Mirzoyan, R, Nakajima, D, Nowak, N, Orito, R, Prada, F, Prandini, E, Scalzotto, V, Shore, S N, Sitarek, J, Stamerra, A, Steinbring, T, Storz, J, Sun, S, Tavecchio, F, Torres, D F, Uellenbeck, M, Zandanel, F, Archambault, S, Bird, R, Cerruti, M, Ciupik, L, Dumm, J, Falcone, A, Feng, Q, Fleischhack, H, tson, L, Kaaret, P, Kieda, D, Krawczynski, H, Kumar, S, Lang, M J, Mukherjee, R, Quinn, J, Ragan, K, Rovero, A C, Staszak, D, Theiling, M, Tyler, J, Varlotta, A, Wakely, S P, Williams, D A, Zitzer, B, collaborators, External, Aller, M F, Chen, W P, Lähteenmäki, A, Lin, C S, Nikolashvili, M G, A Carrami\ nana, Fuhrmann, L, Krichbaum, T P, Moody, J W, Maccaferri, G, Pearson, R, Richards, J L, Sakamoto, T, Tornikoski, M, Yatsu, Y
• Format: Article
• Language: English
• Subjects: Correlation analysis; Crab nebula; Electron energy distribution; Emission; Fluxes; Gamma rays; Light curve; Time lag; Wavelengths; X ray spectra; X-rays
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1502.02650

We performed a 4.5-month multi-instrument campaign (from radio to VHE gamma rays) on Mrk421 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. 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. 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 Mrk421 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.