University Of Tasmania
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A multi-wavelength polarimetric study of the Blazar CTA 102 during a gamma-ray flare in 2012

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journal contribution
posted on 2023-05-18, 16:08 authored by Casadio, C, Gomez, JL, Jorstad, SG, Marscher, AP, Larionov, VM, Smith, PS, Gurwell, MA, Lahteenmaki, A, Agudo, I, Molina, SN, Bala, V, Joshi, M, Taylor, B, Williamson, KE, Arkharov, AA, Blinov, DA, Borman, GA, Di Paola, A, Grishina, TS, Hagen-Thorn, VA, Itoh, R, Kopatskaya, EN, Larionova, EG, Larionova, LV, Morozova, DA, Rastorgueva-Foi, E, Sergeev, SG, Tornikoski, M, Troitsky, IS, Thum, C, Wiesemeyer, H
We perform a multi-wavelength polarimetric study of the quasar CTA 102 during an extraordinarily bright γ-ray outburst detected by the Fermi Large Area Telescope in 2012 September–October when the source reached a flux of F>100 MeV = 5.2 ± 0.4 × 10−6 photons cm−2 s−1. At the same time, the source displayed an unprecedented optical and near-infrared (near-IR) 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 2007 June to 2014 June. We find that the γ-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 γ-ray emission is associated with a change in direction of the jet, which became oriented more closely to our line of sight (θ ~ 12) during the ejection of the knot and the γ-ray outburst. During the flare, the optical polarized emission displays intra-day variability and a clear clockwise rotation of electric vector position angles (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 γ-ray outburst a short distance downstream of the radio core, parsecs from the black hole. This suggests that synchrotron self-Compton scattering of NIR to ultraviolet photons is the probable mechanism for the γ-ray production.


Publication title

Astrophysical Journal



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School of Natural Sciences


Univ Chicago Press

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1427 E 60Th St, Chicago, USA, Il, 60637-2954

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© 2015. The American Astronomical Society. All rights reserved.

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  • Open

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Expanding knowledge in the physical sciences