J/A+A/544/A34 Bright AGN VLBI imaging study at 2 and 8GHz (Pushkarev+, 2012)
Single-epoch VLBI imaging study of bright active galactic nuclei at 2 and 8 GHz.
Pushkarev A.B., Kovalev Y.Y.
<Astron. Astrophys. 544, A34 (2012)>
=2012A&A...544A..34P 2012A&A...544A..34P
ADC_Keywords: Galaxies, radio ; Interferometry ; VLBI
Keywords: galaxies: active - galaxies: jets - quasars: general -
radio continuum: galaxies
Abstract:
We investigate statistical and individual astrophysical properties of
active galactic nuclei (AGNs), such as parsec-scale flux density, core
dominance, angular and linear sizes, maximum observed brightness
temperatures of VLBI core components, spectral index distributions for
core and jet components, and evolution of brightness temperature along
the jets. Furthermore, we statistically compare core flux densities
and brightness temperature as well as jet spectral indices of
γ-ray bright and weak sources.
We used 19 very long baseline interferometry (VLBI) observing sessions
carried out simultaneously at 2.3GHz and 8.6GHz with the participation
of 10 Very Long Baseline Array (VLBA) stations and up to 10 additional
geodetic telescopes. The observations span the period 1998-2003.
We present here single-epoch results from high-resolution radio
observations of 370 AGNs. Our VLBI images at 2.3GHz and 8.6GHz as well
as Gaussian models are presented and analyzed. At least one-fourth of
the cores are completely unresolved on the longest baselines of the
global VLBI observations. The VLBI core components are partially
opaque with the median value of spectral index of alphacore∼0.3,
while the jet features are usually optically thin alphajet~-0.7. The
spectral index typically decreases along the jet ridge line owing to
the spectral aging, with a median value of -0.05mas-1. Brightness
temperatures are found to be affected by Doppler boosting and reach up
to ∼1013K with a median of ∼2.5x1011K at both frequencies. The
brightness temperature gradients along the jets typically follow a
power law Tb∼r-2.2 at both frequencies. We find that 147 sources
(40%) positionally associated with gamma-ray detections from the Fermi
LAT Second Source Catalog have higher core flux densities and
brightness temperatures, and are characterized by the less steep radio
spectrum of the optically thin jet emission.
Description:
File table1 contains the name of the sources and their coordinates,
optical class, redshift, angular scaling, and 2FGL membership. The
parameters of constructed VLBI maps and the corresponding model fits
are presented in the files table5 and table6. The fluxes, sizes, and
brightness temperature for VLBI cores are given in file table7.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 133 370 Parameters of observed sources
table5.dat 84 370 Parameters of VLBI maps
table6.dat 65 2227 Source models (models = same "Name, Date, Freq")
table7.dat 73 370 VLBi core component properties
images/* . 740 FITS maps at 2.3 and 8.6GHz
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Source name (JHHMM+DDMM, J2000)
12- 19 A8 --- IVS Source name (HHMM+DDd, B1950) or usual name
21- 22 I2 h RAh Right Ascension J2000 (hours) (1)
24- 25 I2 min RAm Right Ascension J2000 (minutes) (1)
27- 35 F9.6 s RAs Right Ascension J2000 (seconds) (1)
37 A1 - DE- Declination J2000 (sign) (1)
38- 39 I2 deg DEd Declination J2000 (degrees) (1)
41- 42 I2 arcmin DEm Declination J2000 (minutes) (1)
44- 51 F8.5 arcsec DEs Declination J2000 (seconds) (1)
53 A1 --- cl [QBGU] Optical classification, as Quasar,
BL Lac, Galaxy or Unindentified
55- 60 F6.3 --- z ?=-1.000 Redshift
62- 67 F6.3 pc/mas scale ?=-1.000 Angular scaling conversion
69 A1 --- 2FGL ? Fermi LAT detection flag (2)
71-101 A31 --- Smap Name of the fits file with 2.3GHz map in
subdirectory images
103-133 A31 --- Xmap Name of the fits file with 8.6GHz map in
subdirectory images
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Note (1): The coordinate positions are taken from the Radio Fundamental Catalog
(http://astrogeo.org/rfc) as derived from analysis of all VLBI observations
made in absolute astrometry and geodesy mode
Note (2): Membership in the Fermi LAT Second Source Catalog according to
Abdo et al., 2012, Cat. J/ApJS/199/31.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Source name (JHHMM+DDMM, J2000)
12- 15 F4.2 Jy Speak Peak flux density in 2.3GHz image (in Jy/beam)
17- 21 F5.2 mJy Slev Bottom level contour in 2.3GHz image
23- 26 F4.2 Jy Stot Total flux density from 2.3GHz map
28- 32 F5.2 Jy Sun ?=-1.00 Flux density from the most compact
(unresolved) component on 2.3GHz map
34- 38 F5.2 mas Sbmin FWHM minor axis of restoring beam at 2.3GHz
40- 44 F5.2 mas Sbmaj FWHM major axis of restoring beam at 2.3GHz
46- 48 I3 deg Sbpa Position angle of major axis of restoring beam
at 2.3GHz
50- 53 F4.2 Jy Xpeak Peak flux density in 8.6GHz image (in Jy/beam)
55- 59 F5.2 mJy Xlev Bottom level contour in 8.6GHz image
61- 64 F4.2 Jy Xtot Total flux density from 8.6GHz map
66- 70 F5.2 Jy Xun ?=-1.00 Flux density from the most compact
(unresolved) component on 8.6GHz map
72- 75 F4.2 mas Xbmin FWHM minor axis of restoring beam at 8.6GHz
77- 80 F4.2 mas Xbmaj FWHM major axis of restoring beam at 8.6GHz
82- 84 I3 deg Xbpa Position angle of major axis of restoring beam
at 8.6GHz
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Source name (JHHMM+DDMM, J2000)
12- 21 A10 "YYYY/MM/DD" Date Date of observation
23- 25 F3.1 GHz Freq [2.3/8.6] Frequency of observation
27- 30 I4 mJy S Fitted Gaussian flux density
32- 38 F7.3 mas r Position offset from the core component
40- 45 F6.1 deg phi Position angle of component with respect to
the core component
47- 53 F7.3 mas Maj FWHM major axis of fitted Gaussian
55- 58 F4.2 --- Ratio axial ratio of fitted Gaussian
60- 65 F6.1 deg PA [-172/172] Major axis position angle of
fitted Gaussian
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Source name (JHHMM+DDMM, J2000)
12- 21 A10 "YYYY/MM/DD" Epoch Date of observation
23- 26 F4.2 Jy Score Fitted Gaussian core flux density at 2.3GHz
28- 31 F4.2 mas Sfmaj FWHM major axis of the fitted core Gaussian
at 2.3GHz
33 A1 --- l_Sfmin Limit flag on Sfmin (upper limit) (1)
34- 37 F4.2 mas Sfmin FWHM minor axis of the fitted core Gaussian
at 2.3GHz
39 A1 --- l_STb Limit flag on STb (lower limit) (2)
40- 47 E8.3 K STb Core brightness temperature at 2.3GHz
49- 52 F4.2 Jy Xcore Fitted Gaussian core flux density at 8.6GHz
54- 57 F4.2 mas Xfmaj FWHM major axis of the fitted core Gaussian
at 8.6GHz
59 A1 --- l_Xfmin Limit flag on Xfmin (upper limit) (1)
60- 63 F4.2 mas Xfmin FWHM minor axis of the fitted core Gaussian
at 8.6GHz
65 A1 --- l_XTb Limit flag on XTb (lower limit) (2)
66- 73 E8.3 K XTb Core brightness temperature at 8.6GHz
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Note (1): < means that the upper limit of the minor axis of the fitted core
Gaussian is presented in the following column.
Note (2): > means that the lower limit of the brightness temperature is
presented in the following column.
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Acknowledgements:
Alexander Pushkarev, pushkarev.alexander(at)gmail.com
(End) Alexander Pushkarev [MPIfR, Germany], Patricia Vannier [CDS] 21-Jun-2012