First multi-wavelength campaign on the gamma-ray-loud active galaxy IC 310

Context. The extragalactic very-high-energy gamma-ray sky is rich inblazars. These are jetted active galactic nuclei that are viewed at asmall angle to the line-of-sight. Only a handful of objects viewed at alarger angle are so far known to emit above 100 GeV. Multi-wavelengthstudies of such objects up to the highest energies provide new insightsinto the particle and radiation processes of active galactic nuclei.
Aims: We aim to report the results from the first multi-wavelengthcampaign observing the TeV detected nucleus of the active galaxy IC 310,whose jet is observed at a moderate viewing angle of 10°-20°. Methods: The multi-instrument campaign was conducted between 2012November and 2013 January, and involved observations with MAGIC, Fermi,INTEGRAL, Swift, OVRO, MOJAVE and EVN. These observations werecomplemented with archival data from the AllWISE and 2MASS catalogs. Aone-zone synchrotron self-Compton model was applied to describe thebroadband spectral energy distribution.
Results: IC 310 showed anextraordinary TeV flare at the beginning of the campaign, followed by alow, but still detectable TeV flux. Compared to previous measurements inthis energy range, the spectral shape was found to be steeper during thelow emission state. Simultaneous observations in the soft X-ray bandshowed an enhanced energy flux state and a harder-when-brighter spectralshape behavior. No strong correlated flux variability was found in otherfrequency regimes. The broadband spectral energy distribution obtainedfrom these observations supports the hypothesis of a double-humpstructure.
Conclusions: The harder-when-brighter trend in theX-ray and VHE emission, observed for the first time during thiscampaign, is consistent with the behavior expected from a synchrotronself-Compton scenario. The contemporaneous broadband spectral energydistribution is well described with a one-zone synchrotron self-Comptonmodel using parameters that are comparable to those found for othergamma-ray-emitting misaligned blazars.