Exceptional outburst of the blazar CTA 102 in 2012: The GASP-WEBT campaign and its extension
V.M. Larionov, M. Villata, C.M. Raiteri, S.G. Jorstad, A.P. Marscher,, I. Agudo, P.S. Smith, J.A. Acosta-Pulido, M.J. Ar\'evalo, A.A. Arkharov, R., Bachev, D.A. Blinov, G. Borisov, G.A. Borman, V. Bozhilov, A. Bueno, M.I., Carnerero, D. Carosati, C. Casadio, W.P. Chen

TL;DR
The 2012 outburst of blazar CTA 102 was extensively observed across multiple wavelengths, revealing co-spatial optical and gamma-ray emission, with flux relationships and polarization changes explained by jet dynamics and Doppler effects.
Contribution
This study provides a comprehensive multi-wavelength analysis of CTA 102's 2012 outburst, highlighting the co-spatial emission regions and the impact of Doppler factor variations on observed flux relationships.
Findings
Optical and gamma-ray emissions are co-spatial with a ~1 hour lag.
Gamma-ray and optical fluxes follow SSC mechanism with different relations during outburst and post-outburst.
Spectral hardening correlates with increased Doppler shift and jet orientation changes.
Abstract
After several years of quiescence, the blazar CTA 102 underwent an exceptional outburst in 2012 September-October. The flare was tracked from gamma-ray to near-infrared frequencies, including Fermi and Swift data as well as photometric and polarimetric data from several observatories. An intensive GASP-WEBT collaboration campaign in optical and NIR bands, with an addition of previously unpublished archival data and extension through fall 2015, allows comparison of this outburst with the previous activity period of this blazar in 2004-2005. We find remarkable similarity between the optical and gamma-ray behaviour of CTA 102 during the outburst, with a time lag between the two light curves of ~1 hour, indicative of co-spatiality of the optical and gamma-ray emission regions. The relation between the gamma-ray and optical fluxes is consistent with the SSC mechanism, with a quadratic…
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