Lien, A.Y.et al.2021-01-052021-01-052020-12-08Lien, A.Y.; et al.; Multiwavelength variability and correlation studies of Mrk 421 during historically low X-ray and γ-ray activity in 2015–2016; Monthly Notices of the Royal Astronomical Society (2020); https://academic.oup.com/mnras/advance-article-abstract/doi/10.1093/mnras/staa3727/6027705?redirectedFrom=fulltexthttps://doi.org/10.1093/mnras/staa3727http://hdl.handle.net/11603/20297V A Acciari, S Ansoldi, L A Antonelli, K Asano, A Babić, B Banerjee, A Baquero, U Barres de Almeida, J A Barrio, J Becerra González, W Bednarek, L Bellizzi, E Bernardini, M Bernardos, A Berti, J Besenrieder, W Bhattacharyya, C Bigongiari, O Blanch, G Bonnoli, Ž Bošnjak, G Busetto, R Carosi, G Ceribella, M Cerruti, Y Chai, A Chilingarian, S Cikota, S M Colak, E Colombo, J L Contreras, J Cortina, S Covino, G D’Amico, V D’Elia, P Da Vela, F Dazzi, A De Angelis, B De Lotto, M Delfino, J Delgado, C Delgado Mendez, D Depaoli, T Di Girolamo, F Di Pierro, L Di Venere, E Do Souto Espi neira, D Dominis Prester, A Donini, M Doro, V Fallah Ramazani, A Fattorini, G Ferrara, L Foffano, M V Fonseca, L Font, C Fruck, S Fukami, R J García López, M Garczarczyk, S Gasparyan, M Gaug, N Giglietto, F Giordano, P Gliwny, N Godinović, J G Green, D Green, D Hadasch, A Hahn, L Heckmann, J Herrera, J Hoang, D Hrupec, M Hütten, T Inada, S Inoue, K Ishio, Y Iwamura, J Jormanainen, L Jouvin, Y Kajiwara, M Karjalainen, D Kerszberg, Y Kobayashi, H Kubo, J Kushida, A Lamastra, D Lelas, F Leone, E Lindfors, S Lombardi, F Longo, M López, R López-Coto, A López-Oramas, S Loporchio, B Machado de Oliveira Fraga, C Maggio, P Majumdar, M Makariev, M Mallamaci, G Maneva, M Manganaro, L Maraschi, M Mariotti, M Martínez, D Mazin, S Mender, S Mićanović, D Miceli, T Miener, M Minev, J M Miranda, R Mirzoyan, E Molina, A Moralejo, D Morcuende, V Moreno, E Moretti, P Munar-Adrover, V Neustroev, C Nigro, K Nilsson, D Ninci, K Nishijima, K Noda, S Nozaki, Y Ohtani, T Oka, J Otero-Santos, M Palatiello, D Paneque, R Paoletti, J M Paredes, L Pavletić, P Pe nil, C Perennes, M Persic, P G Prada Moroni, E Prandini, C Priyadarshi, I Puljak, W Rhode, M Ribó, J Rico, C Righi, A Rugliancich, L Saha, N Sahakyan, T Saito, S Sakurai, K Satalecka, B Schleicher, K Schmidt, T Schweizer, J Sitarek, I Šnidarić, D Sobczynska, A Spolon, A Stamerra, D Strom, M Strzys, Y Suda, T Surić, M Takahashi, F Tavecchio, P Temnikov, T Terzić, M Teshima, N Torres-Albà, L Tosti, S Truzzi, J van Scherpenberg, G Vanzo, M Vazquez Acosta, S Ventura, V Verguilov, C F Vigorito, V Vitale, I Vovk, M Will, D Zarić, A Arbet-Engels, D Baack, M Balbo, M Beck, N Biederbeck, A Biland, T Bretz, K Bruegge, J Buss, D Dorner, D Elsaesser, D Hildebrand, R Iotov, M Klinger, K Mannheim, D Neise, A Neronov, M Noethe, A Paravac, W Rhode, B Schleicher, V Sliusar, F Theissen, R Walter, J Valverde, D Horan, M Giroletti, M Perri, F Verrecchia, C Leto, A C Sadun, J W Moody, M Joner, A P Marscher, S G Jorstad, A Lähteenmäki, M Tornikoski, V Ramakrishnan, E Järvelä, R J C Vera, S Righini, A Y LienWe 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 (F2 ₋₁₀ₖₑᵥ < 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 HRₜₑᵥshow 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.2 filesen-USThis item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of record Lien, A.Y.; et al.; Multiwavelength variability and correlation studies of Mrk 421 during historically low X-ray and γ-ray activity in 2015–2016; Monthly Notices of the Royal Astronomical Society (2020); https://academic.oup.com/mnras/advance-articleabstract/doi/10.1093/mnras/staa3727/6027705?redirectedFrom=fulltext is available online at: https://academic.oup.com/mnras/advance-articleabstract/doi/10.1093/mnras/staa3727/6027705?redirectedFrom=fulltext.Text