Carnerero, M. I.; Raiteri, C. M.; Villata, M.; Acosta-Pulido, J. A.; Larionov, V. M.; Smith, P. S.; D'Ammando, F.; Agudo, I.; Arévalo, M. J.; Bachev, R.; Barnes, J.; Boeva, S.; Bozhilov, V.; Carosati, D.; Casadio, C.; Chen, W. P.; Damljanovic, G.; Eswaraiah, E.; Forné, E.; Gantchev, G.; Gómez, J. L.; González-Morales, P. A.; Griñón-Marín, A. B.; Grishina, T. S.; Holden, M.; Ibryamov, S.; Joner, M. D.; Jordan, B.; Jorstad, S. G.; Joshi, M.; Kopatskaya, E. N.; Koptelova, E.; Kurtanidze, O. M.; Kurtanidze, S. O.; Larionova, E. G.; Larionova, L. V.; Latev, G.; Lázaro, C.; Ligustri, R.; Lin, H. C.; Marscher, A. P.; Martínez-Lombilla, C.; McBreen, B.; Mihov, B.; Molina, S. N.; Moody, J. W.; Morozova, D. A.; Nikolashvili, M. G.; Nilsson, K.; Ovcharov, E.; Pace, C.; Panwar, N.; Pastor Yabar, A.; Pearson, R. L.; Pinna, F.; Protasio, C.; Rizzi, N.; Redondo-Lorenzo, F. J.; Rodríguez-Coira, G.; Ros, J. A.; Sadun, A. C.; Savchenko, S. S.; Semkov, E.; Slavcheva-Mihova, L.; Smith, N.; Strigachev, A.; Troitskaya, Yu. V.; Troitsky, I. S.; Vasilyev, A. A.; Vince, O.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 472, Issue 4, p.3789-3804
Description
We report on long-term multiwavelength monitoring of blazar Mrk 421 by
the GLAST-AGILE Support Program of the Whole Earth Blazar Telescope
(GASP-WEBT) collaboration and Steward Observatory, and by the Swift and
Fermi satellites. We study the source behaviour in the period 2007-2015,
characterized by several extreme flares. The ratio between the optical,
X-ray and γ-ray fluxes is very variable. The γ-ray flux
variations show a fair correlation with the optical ones starting from
2012. We analyse spectropolarimetric data and find wavelength-dependence
of the polarization degree (P), which is compatible with the presence of
the host galaxy, and no wavelength dependence of the electric vector
polarization angle (EVPA). Optical polarimetry shows a lack of simple
correlation between P and flux and wide rotations of the EVPA. We build
broad-band spectral energy distributions with simultaneous near-infrared
and optical data from the GASP-WEBT and ultraviolet and X-ray data from
the Swift satellite. They show strong variability in both flux and X-ray
spectral shape and suggest a shift of the synchrotron peak up to a
factor of ˜50 in frequency. The interpretation of the flux and
spectral variability is compatible with jet models including at least
two emitting regions that can change their orientation with respect to
the line of sight.
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