%0 Journal Article %T A multi-wavelength polarimetric study of the blazar CTA 102 during a Gamma-ray flare in 2012 %A Carolina Casadio %A Jos¨¦ L. G¨®mez %A Svetlana G. Jorstad %A Alan P. Marscher %A Valeri M. Larionov %A Paul S. Smith %A Mark A. Gurwell %A Anne L£¿hteenm£¿ki %A Iv¨¢n Agudo %A Sol N. Molina %A Vishal Bala %A Manasvita Joshi %A Brian Taylor %A Karen E. Williamson %A Arkady A. Arkharov %A Dmitry A. Blinov %A George A. Borman %A Andrea Di Paola %A Tatiana S. Grishina %A Vladimir A. Hagen-Thorn %A Ryosuke Itoh %A Evgenia N. Kopatskaya %A Elena G. Larionova %A Liudmila V. Larionova %A Daria A. Morozova %A Elizaveta Rastorgueva-Foi %A Sergey G. Sergeev %A Merja Tornikoski %A Ivan S. Troitsky %A Clemens Thum %A Helmut Wiesemeyer %J Physics %D 2015 %I arXiv %R 10.1088/0004-637X/813/1/51 %X We perform a multi-wavelength polarimetric study of the quasar CTA 102 during an extraordinarily bright $\gamma$-ray outburst detected by the {\it Fermi} Large Area Telescope in September-October 2012 when the source reached a flux of F$_{>100~\mathrm{MeV}} =5.2\pm0.4\times10^{-6}$ photons cm$^{-2}$ s$^{-1}$. At the same time the source displayed an unprecedented optical and NIR outburst. We study the evolution of the parsec scale jet with ultra-high angular resolution through a sequence of 80 total and polarized intensity Very Long Baseline Array images at 43 GHz, covering the observing period from June 2007 to June 2014. We find that the $\gamma$-ray outburst is coincident with flares at all the other frequencies and is related to the passage of a new superluminal knot through the radio core. The powerful $\gamma$-ray emission is associated with a change in direction of the jet, which became oriented more closely to our line of sight ($\theta\sim$1.2$^{\circ}$) during the ejection of the knot and the $\gamma$-ray outburst. During the flare, the optical polarized emission displays intra-day variability and a clear clockwise rotation of EVPAs, which we associate with the path followed by the knot as it moves along helical magnetic field lines, although a random walk of the EVPA caused by a turbulent magnetic field cannot be ruled out. We locate the $\gamma$-ray outburst a short distance downstream of the radio core, parsecs from the black hole. This suggests that synchrotron self-Compton scattering of near-infrared to ultraviolet photons is the probable mechanism for the $\gamma$-ray production. %U http://arxiv.org/abs/1508.07254v2