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تسجيل مستخدم جديدMultiwavelength variability and correlation studies of Mrk 421 during historically low X-ray and $gamma$-ray activity in 2015$-$2016
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We report a characterization of the multi-band flux variability and correlations of the nearby (z=0.031) blazar Markarian 421 (Mrk 421) using data from Mets{a}hovi, Swift, Fermi-LAT, MAGIC, FACT and other collaborations and instruments from November 2014 till June 2016. Mrk 421 did not show any prominent flaring activity, but exhibited periods of historically low activity above 1 TeV (F$_{>1mathrm{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 additional spectral component beyond the regular synchrotron emission. The highest flux variability occurs in X-rays and very-high-energy (E$>$0.1 TeV) $gamma$-rays, which, despite the low activity, show a significant positive correlation with no time lag. The HR$_mathrm{keV}$ and HR$_mathrm{TeV}$ 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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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 collabora
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Multi-wavelength campaigns have been carried out to study the correlation between the very high energy (VHE) $gamma$-ray and the X-ray emissions in blazars but, no conclusive results have been achieved yet. In this paper, we add Milagro data to the e
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