Multiwavelength variability and correlation studies of Mrk 421 during historically low X-ray and γ-ray activity in 2015–2016
Acciari, V.A.; Ansoldi, S.; Antonelli, L.A.; Asano, K.; Babić, A.; Banerjee, B.; Baquero, A.; de Almeida, U. Barres; Barrio, J.A.; González, J. Becerra; Bednarek, W.; Bellizzi, L.; Bernardini, E.; Bernardos, M.; Berti, A.; Besenrieder, J.; Bhattacharyya, W.; Bigongiari, C.; Blanch, O.; Bonnoli, G.; Bošnjak, Ž.; Busetto, G.; Carosi, R.; Ceribella, G.; Cerruti, M.; Chai, Y.; Chilingarian, A.; Cikota, S.; Colak, S.M.; Colombo, E.; Contreras, J.L.; Cortina, J.; Covino, S.; D’Amico, G.; D’Elia, V.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; Delfino, M.; Delgado, J.; Mendez, C. Delgado; Depaoli, D.; Girolamo, T. Di; Pierro, F. Di; Venere, L. Di; Espi neira, E. Do Souto; Prester, D. Dominis; Donini, A.; Doro, M.; Ramazani, V. Fallah; Fattorini, A.; Ferrara, G.; Foffano, L.; Fonseca, M.V.; Font, L.; Fruck, C.; Fukami, S.; López, R.J. García; Garczarczyk, M.; Gasparyan, S.; Gaug, M.; Giglietto, N.; Giordano, F.; Gliwny, P.; Godinović, N.; Green, J.G.; Green, D.; Hadasch, D.; Hahn, A.; Heckmann, L.; Herrera, J.; Hoang, J.; Hrupec, D.; Hütten, M.; Inada, T.; Inoue, S.; Ishio, K.; Iwamura, Y.; Jormanainen, J.; Jouvin, L.; Kajiwara, Y.; Karjalainen, M.; Kerszberg, D.; Kobayashi, Y.; Kubo, H.; Kushida, J.; Lamastra, A.; Lelas, D.; Leone, F.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; López-Oramas, A.; Loporchio, S.; Fraga, B. Machado de Oliveira; Maggio, C.; Majumdar, P.; Makariev, M.; Mallamaci, M.; Maneva, G.; Manganaro, M.; Maraschi, L.; Mariotti, M.; Martínez, M.; Mazin, D.; Mender, S.; Mićanović, S.; Miceli, D.; Miener, T.; Minev, M.; Miranda, J.M.; Mirzoyan, R.; Molina, E.; Moralejo, A.; Morcuende, D.; Moreno, V.; Moretti, E.; Munar-Adrover, P.; Neustroev, V.; Nigro, C.; Nilsson, K.; Ninci, D.; Nishijima, K.; Noda, K.; Nozaki, S.; Ohtani, Y.; Oka, T.; Otero-Santos, J.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J.M.; Pavletić, L.; Penil, P.; Perennes, C.; Persic, M.; Moroni, P.G .Prada; Prandini, E.; Priyadarshi, C.; Puljak, I.; Rhode, W.; Ribó, M.; Rico, J.; Righi, C.; Rugliancich, A.; Saha, L.; Sahakyan, N.; Saito, T.; Sakurai, S.; Satalecka, K.; Schleicher, B.; Schmidt, K.; Schweizer, T.; Sitarek, J.; Šnidarić, I.; Sobczynska, D.; Spolon, A.; Stamerra, A.; Strom, D.; Strzys, M.; Suda, Y.; Surić, T.; Takahashi, M.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Teshima, M.; Torres-Albà, N.; Tosti, L.; Truzzi, S.; van Scherpenberg, J.; Vanzo, G.; Acosta, M. Vazquez; Ventura, S.; Verguilov, V.; Vigorito, C.F.; Vitale, V.; Vovk, I.; Will, M.; Zarić, D.; Arbet-Engels, A.; Baack, D.; Balbo, M.; Beck, M.; Biederbeck, N.; Biland, A.; Bretz, T.; Bruegge, K.; Buss, J.; Dorner, D.; Elsaesser, D.; Hildebrand, D.; Iotov, R.; Klinger, M.; Mannheim, K.; Neise, D.; Neronov, A.; Noethe, M.; Paravac, A.; Rhode, W.; Schleicher, B.; Sliusar, V.; Theissen, F.; Walter, R.; Valverde, J.; Horan, D.; Giroletti, M.; Perri, M.; Verrecchia, F.; Leto, C.; Sadun, A.C.; Moody, J.W.; Joner, M.; Marscher, Alan P.; Jorstad, S.G.; Lähteenmäki, A.; Tornikoski, M.; Ramakrishnan, V.; Järvelä, E.; Vera, R.J.C.; Righini, S.; Lien, A.Y.
We report a characterization of the multi-band flux variability and correlations of the nearby (z=0.031) blazar Markarian 421 (Mrk 421) using data from Metsähovi, Swift, Fermi-LAT, MAGIC, FACT and other collaborations and instruments from November 2014 till June 2016. Mrk 421 did not show any prominent flaring activity, but exhibited periods of historically low activity above 1 TeV (F_> 1TeV < 1.7× 10^−12 ph cm^−2 s^−1) and in the 2-10 keV (X-ray) band (F_2 − 10 keV < 3.6 × 10^−11 erg cm^−2 s^−1), during which the Swift-BAT data suggests an additional spectral component beyond the regular synchrotron emission.The highest flux variability occurs in X-rays and very-high-energy (E > 0.1 TeV) γ-rays, which, despite the low activity, show a significant positive correlation with no time lag. The HRkeV and HRTeV show the harder-when-brighter trend observed in many blazars, but the trend flattens at the highest fluxes, which suggests a change in the processes dominating the blazar variability. Enlarging our data set with data from years 2007 to 2014, we measured a positive correlation between the optical and the GeV emission over a range of about 60 days centered at time lag zero, and a positive correlation between the optical/GeV and the radio emission over a range of about 60 days centered at a time lag of 43^+9_-6 days.This observation is consistent with the radio-bright zone being located about 0.2 parsec downstream from the optical/GeV emission regions of the jet. The flux distributions are better described with a LogNormal function in most of the energy bands probed, indicating that the variability in Mrk 421 is likely produced by a multiplicative process.
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