The Outburst of the Blazar S5 0716+71 in 2011 October: Shock in a Helical Jet

Abstract

We present the results of optical (R band) photometric and polarimetric monitoring and Very Long Baseline Array (VLBA) imaging of the blazar S5 0716+714 along with Fermi γ -ray data during a multi-waveband outburst in 2011 October. We analyze total and polarized intensity images of the blazar obtained with the VLBA at 43 GHz during and after the outburst. Monotonic rotation of the linear polarization vector at a rate of 50 • per night coincided with a sharp maximum in γ -ray and optical flux. At the same time, within the uncertainties, a new superluminal knot appeared with an apparent speed of 21 ± 2c. The general multi-frequency behavior of the outburst can be explained within the framework of a shock wave propagating along a helical path in the blazar's jet.

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“…We have identified 3 stationary features at distances of ∼ 0.06, ∼ 0.13 and ∼ 0.5 mas from the core. As we have reported in [9], knot K5 appeared at MJD ∼ 55850, which coincides within 1σ uncertainty with the time of the highest peak in the γ-ray light curve. and ∼ 55757 no moving components were detected, but the flux of the 7 mm core increased significantly (Fig.1).…”

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“…In one of them, the magnetic field can be tangled and the moving shock compresses and partially orders the tangled magnetic field [4]. The rotation of the EVPA is then coupled to the bent motion of the shock front [10,11]. In the other one the magnetic field is ordered -either helical or toroidal -and the feature 'highlights' different parts of the magnetic field, resulting in an EVPA swing [5,12].…”

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