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 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 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:
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RA (2000) DE Designation(s)
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13 10 28.66 +32 20 43.8 QSO B1308+326 = 5C 12.659
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 70 50 List of 1308+326 15GHz ps images
images/* . 50 Individual ps images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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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
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Acknowledgements:
Silke Britzen, sbritzen(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 15-Feb-2017