J/A+A/604/A111 22GHz image of 3C 273 (Bruni+, 2017)
Probing the innermost regions of AGN jets and their magnetic fields with
RadioAstron. II. Observations of 3C 273 at minimum activity.
Bruni G., Gomez J.L., Casadio C., Lobanov A., Kovalev Y.Y., Sokolovsky K.V.,
Lisakov M.M., Bach U., Marscher A., Jorstad S., Anderson J.M.,
Krichbaum T.P., Savolainen T., Vega-Garcia L., Fuentes A., Zensus J.A.,
Alberdi A., Lee S.-S., Lu R.-S., Perez-Torres M., Ros E.
<Astron. Astrophys. 604, A111 (2017)>
=2017A&A...604A.111B 2017A&A...604A.111B (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Magnetic fields ; Radio sources
Keywords: galaxies: active - galaxies: jets - galaxies: magnetic fields
Abstract:
RadioAstron is a 10m orbiting radio telescope mounted on the Spektr-R
satellite, launched in 2011, performing Space Very Long Baseline
Interferometry (SVLBI) observations supported by a global ground array
of radio telescopes. With an apogee of ∼350000km, it is offering for
the first time the possibility to perform as-resolution imaging in the
cm-band.
The RadioAstron Active Galactic Nuclei (AGN) polarization Key Science
Project (KSP) aims at exploiting the unprecedented angular resolution
provided by RadioAstron to study jet launching/collimation and
magnetic-field configuration in AGN jets. The targets of our KSP are
some of the most powerful blazars in the sky.
We present observations at 22GHz of 3C 273, performed in 2014,
designed to reach a maximum baseline of approximately nine Earth
diameters. Reaching an angular resolution of 0.3mas, we study a
particularly low-activity state of the source, and estimate the
nuclear region brightness temperature, comparing with the extreme one
detected one year before during the RadioAstron early science
period.We also make use of the VLBA-BU-BLAZAR survey data, at 43GHz,
to study the kinematics of the jet in a ∼1.5-year time window.
We find that the nuclear brightness temperature is two orders of
magnitude lower than the exceptionally high value detected in 2013
with RadioAstron at the same frequency (1.4x1013K, source-frame),
and even one order of magnitude lower than the equipartition value.
The kinematics analysis at 43 GHz shows that a new component was
ejected ∼2 months after the 2013 epoch, visible also in our 22GHz map
presented here. Consequently this was located upstream of the core
during the brightness temperature peak. Fermi-LAT observations for the
period 2010-2014 do not show any gamma-ray flare in conjunction with
the passage of the new component by the core at 43GHz.
These observations confirm that the previously detected extreme
brightness temperature in 3C 273, exceeding the inverse Compton limit,
is a short-lived phenomenon caused by a temporary departure from
equipartition. Thus, the availability of interferometric baselines
capable of providing as angular resolution does not systematically
imply measured brightness temperatures over the known physical limits
for astrophysical sources.
Description:
A global ground array of 22 antennas was used to perform observations,
including VLBA (Sc, Hn, Nl, Fd, La, Kp, Pt, Ov, Br, Mk), EVN (Hh, Mc,
Nt, Tr, Jb, Ef, Ys), Long Baseline Array (-LBA- At, Mp, Ho, Cd), and
two Kvazar antennas (Sv, Zc), plus Kalyazin (managed by ASC, Russia),
and Green Bank (NRAO, USA). The observations took place on January
18-19, 2014, for a total of 16.8 hours, and at three different
frequencies: 15GHz, 22GHz, and 43GHz. RA was involved only for the
22GHz part, while for the other bands only the VLBA was used. Both
the Green Bank and Pushchino tracking station took part in the
experiment. A RA-compatible total bandwidth of 32MHz, split into two
16-MHz IFs, was used. RA was scheduled to observe three consecutive
9.5 minute scans every 1.25 hours, to allow for antenna cooling.
Objects:
-----------------------------------------------------------
RA (2000) DE Designation(s)
-----------------------------------------------------------
12 29 06.70 +02 03 08.7 3C 273 = 1RXS J122906.5+020311
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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 1 Information on FITS image
3C273RA22GHz.fits 2880 1641 RadioAstron FITS image
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See also:
J/A+A/576/A122 : 3C 273 high energy spectrum (Esposito+, 2015)
J/A+A/601/A35 : High-fidelity VLA imaging of 3C273 (Perley+, 2017)
J/ApJS/213/26 : Optical light curves of PHL1811 and 3C273 (Fan+, 2014)
J/ApJS/229/21 : VRI monitoring of the QSO 3C 273 in 2005-2016 (Xiong+, 2017)
J/MNRAS/392/1181 : BV(RI)c photometry of 3C 273 (Dai+, 2009)
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- 23 I4 --- Nx Number of pixels along X-axis
25- 28 I4 --- Ny Number of pixels along Y-axis
30- 39 A10 "date" Obs.dat Observation date
41- 47 F7.4 GHz Freq Observed frequency
49- 52 I4 Kibyte size Size of FITS file
54- 72 A19 --- FileName Name of FITS file
74- 94 A21 --- Title Title of the FITS file
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Acknowledgements:
Gabriele Bruni, bruni(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 24-Jul-2017