J/A+A/672/A130 Blazar 3C 454.3 time variability (Chamani+, 2023)
Time variability of the core-shift effect in the blazar 3C 454.3.
Chamani W., Savolainen T., Ros E., Kovalev Y.Y., Wiik K., Laehteenmaeki A.,
Tornikoski M., Tammi J.
<Astron. Astrophys. 672, A130 (2023)>
=2023A&A...672A.130C 2023A&A...672A.130C (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Active gal. nuclei ; Magnetic fields ; VLBI
Keywords: galaxies: active - galaxies: jets - galaxies: magnetic fields -
quasars: individual: 3C 454.3 - techniques: high angular resolution
Abstract:
Measuring and inferring the key physical parameters of jets in active
galactic nuclei (AGN) requires high-resolution very long baseline
interferometry (VLBI) observations. Using VLBI to measure a core-shift
effect is a common way of obtaining estimates of the jet magnetic
field strength, a key parameter for understanding jet physics. The
VLBI core is typically identified as the bright feature at the
upstream end of the jet, and the position of this feature changes with
the observed frequency, rcore ∝ nu-1/kr_^. Due to the
variable nature of AGN, flares can cause variability of the measured
core shift. In this work, we investigated the time variability of the
core-shift effect in the luminous blazar 3C 454.3. We employed a
self-referencing analysis of multi-frequency (5, 8, 15, 22-24, and
43GHz) Very Long Baseline Array (VLBA) data covering 19 epochs from
2005 to 2010. We found significant core-shift variability ranging from
0.27 to 0.86-milliarcsecond between 5GHz and 43GHz. These results
confirm the core-shift variability phenomenon observed previously.
Furthermore, we also found time variability of the core-shift index,
kr, which was typically below one, with an average value of
0.85±0.08 and a standard deviation of 0.30. Values of kr below one
were found during flaring and quiescent states. Our results indicate
that the commonly assumed conical jet shape and equipartition
conditions do not always hold simultaneously. Even so, these
conditions are typically assumed when deriving magnetic field
strengths from core-shift measurements, which can lead to unreliable
results if kr significantly deviates from unity. Therefore, it is
necessary to verify that kr=1 actually holds before using core-shift
measurements and the equipartition assumption to derive physical
conditions in the jets. When kr=1 epochs are selected in the case of
3C 454.3, the magnetic field estimates are consistent, even though the
core shift varies significantly with time. Subsequently, we estimated
the magnetic flux in the jet of 3C 454.3 and found that the source is
in the magnetically arrested disc state, which agrees with earlier
studies. Finally, we found a good correlation of the core position
with the core flux density, rcore ∝ Score0.7, which is
consistent with increased particle density during the flares.
Description:
We analysed a total of 19 epochs of VLBA data dating from 2005 to 2010
and comprising five different frequency bands: C band (5GHz), X band
(8GHz), KU band (15GHz; hereafter U band), K band (22-24GHz), and Q
band (43GHz). These observations include both our own multi-frequency
monitoring programmes (The first of these programmes (BS157; PI T.
Savolainen) was triggered by the major multi-wavelength flaring event
in May 2005 (Villata et al., 2006A&A...453..817V 2006A&A...453..817V). The second
programme (BW086; PI K. Wiik) was a continuation of the monitoring
started with BS157. The third programme (S2087; PI Y. Y. Kovalev) was
triggered by the Fermi-LAT detected gamma-ray flare in September 2009.
The last monitoring also covered the large gamma-ray outburst of
December 2009 (Ackermann et al., 2010ApJ...721.1383A 2010ApJ...721.1383A).) and archival
data (Public data from the project BO033 (PI S. P. O'Sullivan) was
downloaded from the NRAO archive).
Objects:
---------------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------------
22 53 57.74 +16 08 53.5 3C 454.3 = IERS B2251+158
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 131 154 List of fits images
fits/* . 154 Individual fits images
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See also:
J/ApJ/712/405 : Multiwavelength obs. of 3C 454.3 III. (Vercellone+, 2010)
J/ApJ/763/L36 : MgII and FeII flux of the blazar 3C 454.3 (Leon-Tavares+, 2013)
J/ApJ/856/80 : 6-yr optical monitoring of the FSRQ 3C 454.3 (Fan+, 2018)
J/ApJS/248/8 : 9-yr of Fermi-LAT + Swift obs. of 3C 454.3 flares (Das+, 2020)
J/ApJ/906/5 : 3C 454.3 FeII, MgII + 3000Å meas. (Amaya-Almazan+, 2021)
J/ApJS/253/10 : 12yrs of R-band photometry of the quasar 3C 454.3 (Fan+, 2021)
J/ApJS/257/37 : Multiwav. data for blazars 3C 279 + 3C 454.3 (Paliya+, 2021)
J/ApJS/262/43 : NGT gri monitoring of the FSRQ 3C 454.3 (Yuan+, 2022)
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 "datime" Obs.date Observation date
41- 51 E11.6 Hz Freq Observed frequency
54- 59 I6 Kibyte size Size of FITS file
61-103 A43 --- FileName Name of FITS file, in subdirectory fits
105-131 A27 --- Title Title of the FITS file
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Acknowledgements:
Wara Chamani, nosferatu.wara(at)gmail.com
(End) Patricia Vannier [CDS] 26-Jan-2023