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We report a characterization of the multi-band flux variability andcorrelations of the nearby (z=0.031) blazar Markarian 421 (Mrk 421) using datafrom Mets\"{a}hovi, Swift, Fermi-LAT, MAGIC, FACT and other collaborations andinstruments from November 2014 till June 2016. Mrk 421 did not show anyprominent flaring activity, but exhibited periods of historically low activityabove 1 TeV (F$_{>1\mathrm{TeV}}<$ 1.7$\times$10$^{-12}$ ph cm$^{-2}$ s$^{-1}$)and in the 2-10 keV (X-ray) band (F$_{2-10 \mathrm{keV}}<$3.6$\times$10$^{-11}$erg cm$^{-2}$ s$^{-1}$), during which the Swift-BAT data suggests an additionalspectral component beyond the regular synchrotron emission. The highest fluxvariability occurs in X-rays and very-high-energy (E$>$0.1 TeV) $\gamma$-rays,which, despite the low activity, show a significant positive correlation withno time lag. The HR$_\mathrm{keV}$ and HR$_\mathrm{TeV}$ show theharder-when-brighter trend observed in many blazars, but the trend flattens atthe highest fluxes, which suggests a change in the processes dominating theblazar variability. Enlarging our data set with data from years 2007 to 2014,we measured a positive correlation between the optical and the GeV emissionover a range of about 60 days centered at time lag zero, and a positivecorrelation between the optical/GeV and the radio emission over a range ofabout 60 days centered at a time lag of $43^{+9}_{-6}$ days.This observation isconsistent with the radio-bright zone being located about 0.2 parsec downstreamfrom the optical/GeV emission regions of the jet. The flux distributions arebetter described with a LogNormal function in most of the energy bands probed,indicating that the variability in Mrk 421 is likely produced by amultiplicative process.

Multiwavelength variability and correlation studies of Mrk 421 during historically low X-ray and $\gamma$-ray activity in 2015$-$2016