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25 April 2024

» arxiv » 1508.7254

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A multi-wavelength polarimetric study of the blazar CTA 102 during a Gamma-ray flare in 2012
Carolina Casadio ; José L. Gómez ; Svetlana G. Jorstad ; Alan P. Marscher ; Valeri M. Larionov ; Paul S. Smith ; Mark A. Gurwell ; Anne Lähteenmäki ; Iván Agudo ; Sol N. Molina ; Vishal Bala ; Manasvita Joshi ; Brian Taylor ; Karen E. Williamson ; Arkady A. Arkharov ; Dmitry A. Blinov ; George A. Borman ; Andrea Di Paola ; Tatiana S. Grishina ; Vladimir A. Hagen-Thorn ; Ryosuke Itoh ; Evgenia N. Kopatskaya ; Elena G. Larionova ; Liudmila V. Larionova ; Daria A. Morozova ; Elizaveta Rastorgueva-Foi ; Sergey G. Sergeev ; Merja Tornikoski ; Ivan S. Troitsky ; Clemens Thum ; Helmut Wiesemeyer ;
Date:	28 Aug 2015
Abstract:	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$_{>100~mathrm{MeV}} =5.2pm0.4 imes10^{-6}$ 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 ($ hetasim$1.2$^{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.
Source:	arXiv, 1508.7254
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