J/MNRAS/485/1822 AGN core shift measurements (Plavin+, 2019)
Significant core shift variability in parsec-scale jets of
active galactic nuclei.
Plavin A.V., Kovalev Y.Y., Pushkarev A.B., Lobanov A.P.
<Mon. Not. R. Astron. Soc., 485, 1822-1842 (2019)>
=2019MNRAS.485.1822P 2019MNRAS.485.1822P (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei
Keywords: galaxies: active - galaxies: jets - quasars: general -
radio continuum: galaxies - reference systems
Abstract:
The apparent position of jet base (core) in radio-loud active galactic
nuclei changes with frequency because of synchrotron self-absorption.
Studying this 'core shift' effect enables us to reconstruct
properties of the jet regions close to the central engine. We report
here results from core shift measurements in AGNs observed with global
VLBI at 2 and 8GHz at epochs from 1994 to 2016. Our sample contains
40 objects observed at least 10 times during that period. The core
shift is determined using a new automatic procedure introduced to
minimize possible biases. The resulting multiple epoch measurements of
the core position are employed for examining temporal variability of
the core shift. We argue that the core shift variability is a common
phenomenon, as established for 33 of 40 AGNs we study. Our analysis
shows that the typical offsets between the core positions at 2 and
8GHz are about 0.5mas and they vary in time. Typical variability of
the individual core positions is about 0.3mas. The measurements show
a strong dependence between the core position and its flux density,
suggesting that changes in both are likely related to the nuclear
flares injecting denser plasma into the flow. We determine that
density of emitting relativistic particles significantly increases
during these flares, while relative magnetic field changes less and in
the opposite direction.
Description:
AGN core shift measurements based on 2 and 8GHz VLBI observations.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 63 40 Source properties
table2.dat 68 1691 Estimated parameter values
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- J2000 J2000 name from Radio Fundamental Catalogue
(RFC, http://astrogeo.org/rfc) version 2017c
(JHHMM+DDMM)
12- 19 A8 --- B1950 B1950 name (HHMM+DDd)
21- 22 I2 h RAh Right ascension (J2000)
24- 25 I2 min RAm Right ascension (J2000)
27- 33 F7.4 s RAs Right ascension (J2000)
35 A1 --- DE- Declination sign (J2000)
36- 37 I2 deg DEd Declination (J2000)
39- 40 I2 arcmin DEm Declination (J2000)
42- 48 F7.4 arcsec DEs Declination (J2000)
50- 54 F5.3 --- z Redshift from Lister et al.
(2009, Cat. J/AJ/137/3718)
56- 60 F5.1 deg PA jet positional angle estimated as described
in Section 2
62- 63 I2 --- Nobs Number of observational epochs used in our
analysis
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- J2000 J2000 name from RFC (JHHMM+DDMM)
12- 21 A10 "date" Obs.date Epoch of observation
23- 45 F23.20 mas CoreShiftmas 8-2GHz core shift magnitude
in milliarcseconds
47- 68 F22.19 pc CoreShiftpc 8-2GHz core shift magnitude
in parsecs (projected on the sky)
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Acknowledgements:
Alexander Plavin, alexander(at)plav.in
(End) Patricia Vannier [CDS] 28-Aug-2019