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Post Info TOPIC: CTA-102
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CTA-102
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Title: Dense optical and near-infrared monitoring of CTA 102 during high state in 2012 with OISTER: Detection of intra-night "orphan polarised flux flare"
Authors: Ryosuke Itoh, Yasushi Fukazawa, Yasuyuki T. Tanaka, Yuhei Abe, Hiroshi Akitaya, Akira Arai, Masahiko Hayashi, Takafumi Hori, Mizuki Isogai, Hideyuki Izumiura, Koji S. Kawabata, Nobuyuki Kawai, Daisuke Kuroda, Ryo Miyanoshíta, Yuki Moritani, Tomoki Morokuma, Takahiro Nagayama, Jumpei Nakamoto, Chikako Nakata, Yumiko Oasa, Tomohito Ohshima, Takashi Ohsugi, Shin-ichiro Okumura, Yoshihiko Saito, Yu Saito, Mahito Sasada, Kazuhiro Sekiguchi, Yuhei Takagi, Jun Takahashi, Yukihiro Takahashi, Katsutoshi Takaki, Makoto Uemura, Issei Ueno, Seitaro Urakawa, Makoto Watanabe, Masayuki Yamanaka, Yoshinori Yonekura, Michitoshi Yoshida 

CTA 102, classified as a flat spectrum radio quasar at z=1.037, produced exceptionally bright optical flare in 2012 September. Following Fermi-LAT detection of enhanced gamma-ray activity, we densely monitored this source in the optical and near-infrared bands for the subsequent ten nights using twelve telescopes in Japan and South-Africa. On MJD 56197 (2012 September 27, 4-5 days after the peak of bright gamma-ray flare), polarised flux showed a transient increase, while total flux and polarisation angle remained almost constant during the "orphan polarised-flux flare". We also detected an intra-night and prominent flare on MJD 56202. The total and polarised fluxes showed quite similar temporal variations, but PA again remained constant during the flare. Interestingly, the polarisation angles during the two flares were significantly different from the jet direction. Emergence of a new emission component with high polarisation degree (PD) up to 40% would be responsible for the observed two flares, and such a high PD indicates a presence of highly ordered magnetic field at the emission site. We discuss that the well-ordered magnetic field and even the observed directions of polarisation angle which is grossly perpendicular to the jet are reasonably accounted for by transverse shock(s) propagating down the jet. 

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Blobrana


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Posts: 131433
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Title: Core-shift and spectral analysis of the 2006 radio flare in CTA102
Authors: C. M. Fromm, E. Ros, M. Perucho, T. Savolainen, P. Mimica, A. P. Lobanov, J. A. Zensus

The 2006 radio flare in the blazar CTA102 is the largest ever reported for this source. The analysis of the single--dish light curves revealed a possible shock-shock interaction as a scenario for the 2006 outburst. In order to confirm this hypothesis we analysed eight multi-frequency (2 GHz - 86 GHz) VLBI observations covering the 2006 flare. We detected a radio component ejected around 2005.9 and a stationary feature around 0.1 mas away from the core. We also performed a core-shift and spectral analysis on the fully calibrated VLBI maps. The frequency dependent position of the core slightly deviates from the typical \nu^{-1}-dependence during the flaring state. This behaviour may reflect a mismatch between magnetic energy density and energy density of the relativistic particles. From the core-shift corrected maps we obtained the spectral parameters and computed the temporal and spatial evolution of the jet intrinsic parameters such as the magnetic field and the particle density. The overall picture of the source could be best interpreted as an over-pressured jet perturbed by travelling shock waves.

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