J/AJ/162/121 3627 International Celestial Reference Frame sources (Hunt+, 2021)
Imaging sources in the third realization of the International Celestial
Reference Frame.
Hunt L.R., Johnson M.C., Cigan P.J., Gordon D., Spitzak J.
<Astron. J., 162, 121-121 (2021)>
=2021AJ....162..121H 2021AJ....162..121H (SIMBAD/NED BibCode)
ADC_Keywords: QSOs; Active gal. nuclei; Spectra, radio;
Keywords: Astrometry; Astronomical coordinate systems; Active galactic nuclei
Abstract:
The third iteration of the International Celestial Reference Frame
(ICRF3) is made up of 4536 quasars observed at S/X bands using
very-long-baseline interferometry. These sources are high-redshift
quasars, typically between 1<z<2, that are believed to host active
galactic nuclei at their centers. The position of compact radio
sources can be determined better than sources with large amounts of
extended radio structure. Here we report information on a series of 20
observations from 2017 January through December 2017 that were
designed for precise astrometry and to monitor the structure of
sources included in the ICRF3. We targeted 3627 sources over the one
year campaign and found the median flux density of 2697 detected
sources at S band is 0.13Jy, and the median flux density of 3209
sources detected at X band is 0.09Jy. We find that 70% of detected
sources in our campaign are considered compact at X band and ideal for
use in the ICRF and 89% of the 2615 sources detected at both
frequencies have a flat spectral index, α>0.5
Description:
The observations were made using the Very Long Baseline Array (VLBA)
S/X dual frequency system, providing compatibility with earlier VLBA
astrometry sessions and with nearly 40yr of astrometric/geodetic Very
Long Baseline Interferometry (VLBI). Frequencies and bandwidths were
identical to VLBA Calibrator Survey Observations (VCS-II; Gordon+,
J/AJ/151/154), with 12, 32MHz channel windows at X band, and four at S
band, using two-bit sampling for a total recording rate of 2Gbps.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 181 5610 Radio properties of ICRF sources
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See also:
J/A+A/544/A34 : Bright AGN VLBI imaging study at 2 and 8GHz (Pushkarev+, 2012)
J/AJ/150/58 : VLBI ICRF2 (Fey+, 2015)
J/AJ/151/154 : Second epoch VLBA Calibrator Survey (VCS-II) (Gordon+, 2016)
J/A+A/644/A159 : The third realization of the ICRF, ICRF3 (Charlot+, 2020)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- IERS Source IERS Name
10- 30 F21.17 deg RAdeg [0/360] Right ascension (ICRF) at Ep=2015.0 (1)
32- 52 F21.17 deg DEdeg [-50/89] Declination (ICRF) at Ep=2015.0 (1)
54- 57 F4.1 --- alpha [-5.1/4.9]? Clean 2.3GHz to 8.7GHz spectral *
index
59- 59 A1 --- Session Session (2)
61- 64 I4 yr Obs.Y [2017] Observation, year
66- 68 A3 "month" Obs.M Observation, month
70- 71 I2 d Obs.D Observation, day in month
73- 80 F8.6 mJy/beam Srms-t [0.0001/0.008]? 2.3GHz theoretical RMS in image
82- 89 F8.6 mJy/beam Srms [4.1e-5/1.4]? 2.3GHz measured RMS in image
91- 98 F8.6 Jy/beam Speak [7.9e-5/5.6]? 2.3GHz peak flux density
of the brightest pixel
100-107 F8.6 Jy Stot [0.001/7.9]? 2.3GHz total flux density (3)
109-116 F8.6 Jy Sgau [0.003/6.9]? 2.3GHz Gaussian fit flux density
(4)
118-122 F5.1 --- Ssnr [1.2/866]? 2.3GHz Signal-to-noise ratio (5)
124-131 F8.6 mJy/beam Xrms-t [9.1e-5/0.006]? 8.7GHz theoretical RMS in image
133-140 F8.6 mJy/beam Xrms [0.0001/1.9]? 8.7GHz measured RMS in image
142-149 F8.6 Jy/beam Xpeak [0.005/7.2]? 8.7GHz peak flux density of the
brightest pixel
151-158 F8.6 Jy Xtot [0.009/7.6]? 8.7GHz total flux density (3)
160-174 F15.6 Jy Xgau [-1.8e6/7.5]? 8.7GHz Gaussianfit flux density
(4)
176-181 F6.1 --- Xsnr [0.4/1776]? 8.7GHz Signal-to-noise ratio (5)
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Note (1): The Right Ascension and Declination of the source taken from the
ICRF3 catalog (Charlot+, 2020, J/A+A/644/A159) with precision to the
median uncertainty of the frame to 0.1mas
Note (2): Session corresponds to the last character of the individual observing
sessions listed in Table 2, e.g., a=UF001A.
Note (3): Total flux density of the image determined by summing the clean
components.
Note (4): SGau is the flux density calculated from fitting a Gaussian to the
brightest component in an image.
Note (5): S/N is the signal-to-noise ratio of an image calculated as the peak
flux density divided by Srms, the measured RMS in an image.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 08-Dec-2021