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J/A+A/602/A29       QSO 1308+326 at 15GHz modelfit results     (Britzen+, 2017)

A swirling jet in the quasar 1308+326 Britzen S., Qian S.-J., Steffen W., Kun E., Karouzos M., Gergely L., Schmidt J., Aller M., Aller H., Krause M., Fendt C., Bottcher M., Witzel A., Eckart A., Moser L. <Astron. Astrophys. 602, A29 (2017)> =2017A&A...602A..29B (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Interferometry Keywords: quasars: general - techniques: interferometric Abstract: Despite numerous and detailed studies of the jets of Active Galactic Nuclei (AGN) on pc-scales, many questions are still debated. The physical nature of the jet components is one of the most prominent unsolved problems as is the launching mechanism of jets in AGN. The Quasar 1308+326 (z=0.997) allows detailed studies of the overall properties of the jet and to derive a more physical understanding of the nature and origin of jets in general. The long-term data provided by the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) survey permit tracing out the structural changes in 1308+326 presented here. The long-lived jet features in this source can be followed for about two decades. We investigate the VLBI morphology and kinematics of the jet of 1308+326 to understand the physical nature of this jet and jets in general, the role of magnetic fields, and the causal connection between jet features and the launching process. 50 VLBA observations performed at 15GHz from the MOJAVE survey have been re-modeled with Gaussian components and re-analyzed (the time covered: 1995.05-2014.07). The analysis is supplemented by multi-wavelength radio-data (UMRAO, at 4.8, 8.0, and 14.5GHz) in polarization and total intensity. We fit the apparent motion of the jet features with the help of a model of a precessing nozzle. The jet features seem to be emitted with varying viewing angles and launched into an ejection cone. Tracing the component paths yields evidence for rotational motion. Radio flux-density variability can be explained as a consequence of enhanced Doppler boosting corresponding to the motion of the jet relative to the line of sight. Based on the presented kinematics and other indicators, such as electric-vector polarization position angle (EVPA)-rotation we conclude that the jet of 1308+326 has a helical structure, i.e. the components are moving along helical trajectories, while the trajectories themselves are experiencing a precessing motion as well. A model of a precessing nozzle (Qian et al., 2014RAA....14..249Q) was applied to the data and a subset of the observed jet feature paths can be modeled successfully within this model. The data through 2012 are consistent with a swing period of 16.9 years. We discuss several scenarios to explain the observed motion phenomena, including a binary black hole model. It seems unlikely that the accretion disk around the primary black hole, that is disturbed by tidal forces of the secondary black hole, is able to launch a persistent axisymmetric jet. We conclude that we are observing a rotating helix. In particular, the observed EVPA swings can be explained by a shock moving through a straight jet pervaded by a helical magnetic field. We compare our results for 1308+326 with other astrophysical scenarios where similar, wound up filamentary structures are found. They all are related to accretion-driven processes. A helically moving or wound up object is often explained by filamentary features moving along magnetic field lines of magnetic flux tubes. It seems that a "component" is plasma tracing the magnetic field which guides the motion of the radiating radio-band plasma. Further investigations and modeling are in preparation. Description: We re-modeled 50 VLBA observations of 1308+326 obtained at 15GHz (taken from the online MOJAVE archive webpage) between 1995.05 and 2014.07 with Gaussian components within the difmap-modelfit programme (Shepherd 1997). The modelfit programme fits image-plane model components to the visibilities in the uv plane. Every epoch was modeled independently starting from a point source model. The errors were estimated from deviations in all parameters derived by calculating fits to models with ±1 component. All the images with model-fits superimposed are displayed in Figs. 16-28. The parameters and corresponding uncertainties of the model-fits are listed in Tables 2-6 (paper). Components labeled with 'x' denote for features that could not be reliably traced across the epochs. Objects: ----------------------------------------------------- RA (2000) DE Designation(s) ----------------------------------------------------- 13 10 28.66 +32 20 43.8 QSO B1308+326 = 5C 12.659 ----------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file list.dat 70 50 List of 1308+326 15GHz ps images images/* 0 50 Individual ps images
Byte-by-byte Description of file: list.dat
Bytes Format Units Label Explanations
1- 6 F6.3 GHz Freq Observed frequency 8- 17 A10 "date" Obs.date Observation date (YYYY/MM/DD) 20- 33 A14 --- FileName Name of the ps image in subdirectory images 35- 70 A36 --- Title Title of the file
Acknowledgements: Silke Britzen, sbritzen(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 15-Feb-2017
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