J/A+A/569/A115 TANAMI monitoring of Centaurus A. (Muller+, 2014)
TANAMI monitoring of Centaurus A.
The complex dynamics in the inner parsec of an extragalactic jet.
Muller C., Kadler M., Ojha R., Perucho M., Grossberger C., Ros E., Wilms J.,
Blanchard J., Bock M., Carpenter B., Dutka M., Edwards P.G., Hase H.,
Horiuchi S., Kreikenbohm A., Lovell J.E.J., Markowitz A., Phillips C.,
Plotz C., Pursimo T., Quick J., Rothschild R., Schulz R., Steinbring T.,
Stevens J., Trustedt J., Tzioumis A.K.
<Astron. Astrophys. 569, A115 (2014)>
=2014A&A...569A.115M 2014A&A...569A.115M
ADC_Keywords: Active gal. nuclei ; Galaxies, radio ; VLBI
Keywords: galaxies: active - galaxies: individual: Centaurus A -
galaxies: individual: NGC 5128 - techniques: high angular resolution -
galaxies: jets
Abstract:
Centaurus A (Cen A) is the closest radio-loud active galactic nucleus.
Very Long Baseline Interferometry (VLBI) enables us to study the
spectral and kinematic behavior of the radio jet-counterjet system on
milliarcsecond scales, providing essential information for jet
emission and propagation models.
In the framework of the TANAMI monitoring, we investigate the
kinematics and complex structure of Cen A on subparsec scales. We have
been studying the evolution of the central parsec jet structure of Cen
A for over 3.5-years. The proper motion analysis of individual jet
components allows us to constrain jet formation and propagation and to
test the proposed correlation of increased high-energy flux with jet
ejection events. Cen A is an exceptional laboratory for such a
detailed study because its proximity translates to unrivaled linear
resolution, where one milliarcsecond corresponds to 0.018pc.
As a target of the southern-hemisphere VLBI monitoring program TANAMI,
observations of Cen A are done approximately every six months at
8.4GHz with the Australian Long Baseline Array (LBA) and associated
telescopes in Antarctica, Chile, New Zealand, and South Africa,
complemented by quasi-simultaneous 22.3GHz observations.
The first seven epochs of high-resolution TANAMI VLBI observations at
8.4GHz of Cen A are presented, resolving the jet on
(sub-)milliarcsecond scales. They show a differential motion of the
subparsec scale jet with significantly higher component speeds farther
downstream where the jet becomes optically thin. We determined
apparent component speeds within a range of 0.1c to 0.3c and
identified long-term stable features. In combination with the
jet-to-counterjet ratio, we can constrain the angle to the line of
sight to θ∼12°-45°.
The high-resolution kinematics are best explained by a spine-sheath
structure supported by the downstream acceleration occurring where the
jet becomes optically thin. On top of the underlying, continuous flow,
TANAMI observations clearly resolve individual jet features. The flow
appears to be interrupted by an obstacle causing a local decrease in
surface brightness and circumfluent jet behavior. We propose a
jet-star interaction scenario to explain this appearance. The
comparison of jet ejection times to high X-ray flux phases yields a
partial overlap of the onset of the X-ray emission and increasing jet
activity, but the limited data do not support a robust correlation.
Description:
Seven naturally weighted clean-images from TANAMI VLBI observations at
8.4GHz of Centaurus A (Fig. 1 and 2).
Objects:
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RA (2000) DE Designation(s)
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13 25 27.62 -43 01 08.8 Cen A = NGC 5128
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 94 7 List of FITS images
fits/* . 7 Individual VLBI FITS images of Cen A at 8.4GHz
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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- 9 F9.5 deg RAdeg Right ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 F3.1 mas/pix Scale [0.1] Scale of the image
24- 27 I4 --- Nx [1024] Number of pixels along X-axis
28 A1 --- --- [x]
29- 32 I4 --- Ny [1024] Number of pixels along Y-axis
34- 40 F7.5 GHz Freq [8.42/8.45] Frequency
42- 51 A10 "YYYY-MM-DD" ObsDate Observation date
53- 56 I4 Kibyte size [4132/4157] Size of FITS file
58- 68 A11 --- FileName Name of FITS file in subdirectory fits
70- 94 A25 --- Title Title of the file
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Acknowledgements:
Cornelia Muller, cornelia.mueller(at)sternwarte.uni-erlangen.de
(End) Patricia Vannier [CDS] 21-Jul-2014