J/AJ/167/273 MeerKAT calibrator sources polarization properties (Taylor+, 2024)
A MeerKAT Polarization Survey of Southern Calibration Sources.
Taylor A.R., Legodi L.S.
<Astron. J., 167, 273 (2024)>
=2024AJ....167..273T 2024AJ....167..273T
ADC_Keywords: Radio continuum; Interferometry; Active gal. nuclei
Keywords: Radio continuum emission ; Radio interferometry ;
Spectropolarimetry ; Extragalactic radio sources ; Active
galactic nuclei ; Radio sources
Abstract:
We report on full-Stokes L-band observations of 98 MeerKAT calibration
sources. Linear polarization is detected in 71 objects above a
fractional level of 0.2%. We identify ten sources with strong
fractional linear polarization and low Faraday rotation measure that
could be suitable for wide-band absolute polarization calibration. We
detect significant circular polarization from 24% of the sample down
to a detection level of 0.07%. Circularly polarized emission is seen
only for flat spectrum sources α>-0.5. We compare our
polarized intensities and Faraday synthesis results to data from the
NVSS at 1400MHz and the ATCA SPASS survey at 2300MHz. NVSS data
exist for 54 of our sources and SPASS data for 20 sources. The percent
polarization and rotation measures from both surveys agree well with
our results. The residual instrumental linear polarization for these
observations is measured at 0.16%, and the residual instrumental
circular polarization is measured at 0.05%. These levels may reflect
either instabilities in the relative bandpass between the two
polarization channels with either time or antenna orientation, or
atmospheric/ionospheric variations with pointing direction. Tracking
of the hourly gain solutions on J0408-6545 after transfer of the
primary gain solutions suggests a deterioration of the gain stability
by a factor of several starting about 2hr after sunrise. This
suggests that observing during the nighttime could dramatically
improve the precision of polarization calibration.
Description:
The calibration sources were observed with MeerKAT during one of two
observing runs carried out by the SARAO MeerKAT commissioning team.
Both observing runs were about 12hr long. Each target source was
observed for a short scan of about 5minutes.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 124 101 Polarization properties of MeerKAT calibrator
sources
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See also:
VII/2 : Master list of radio sources, updated 1978 (Dixon, 1970)
VIII/38 : The Parkes-MIT-NRAO 4.85GHz (PMN) Surveys (Griffith+ 1993-1996)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VIII/74 : SPECFIND Catalog of radio continuum spectra (Vollmer+ 2005)
VIII/85 : SPECFIND V2.0 Catalog of radio continuum spectra (Vollmer+ 2009)
J/ApJ/702/1230 : Rotation measure image of the sky (Taylor+, 2009)
J/ApJS/212/15 : Polarized NVSS sources SEDs (Farnes+, 2014)
J/ApJ/829/5 : SPASS & NVSS bright extragalactic radio sources (Lamee+, 2016)
J/other/PASA/34.13 : S-PASS catalog at 2.3GHz (Meyers+, 2017)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name J2000-based source name
12- 17 F6.3 Jy S1.4GHz [0.52/16.2] Flux density at 1400MHz from a
power-law fit to the Stokes I spectrum (1)
19- 23 F5.3 Jy e_S1.4GHz [0.001/0.02] Uncertainty in S1.4GHz (1)
25- 30 F6.3 --- alpha [-1.31/1.48] In-band spectral index,
Equation 11 (1)
32- 36 F5.3 --- e_alpha [0.001/0.02] Uncertainty in alpha (1)
38- 43 F6.3 --- C [-0.83/0.68] Curvature term from spectral fit
to the Stokes I spectrum
45- 49 F5.3 --- e_C [0.003/0.04] Uncertainty in C
51- 54 F4.2 % p1400 [0.01/9.9] Percent polarized intensity
at 1400MHz (2)
56- 60 F5.3 % e_p1400 [0.0/0.013] Uncertainty in p1400 (2)
62- 66 F5.1 deg PA1400 [-86.5/84.8] Position angle at 1400 MHz (2)
68- 71 F4.1 deg e_PA1400 [0.1/21.7] Uncertainty in PA1400 (2)
73- 77 F5.2 --- beta [-7.37/3.25] Spectral index of polarized
intensity (3)
79- 82 F4.2 --- e_beta [0.01/0.34] Uncertainty in beta (3)
84- 89 F6.1 rad.m-2 RM [-127/107] Faraday depth of dominant rotation
measure synthesis component
91- 93 F3.1 rad.m-2 e_RM [0.1/2] Uncertainty in RM
95- 98 F4.2 % pmax [0.02/9.39] Amplitude (percent polarization)
of dominant rotation measure synthesis
component
100-105 F6.3 % vmed [-0.23/0.36] Median value fractional Stokes V
over the band (4)
107-111 F5.3 % e_vmed [0.001/0.003] Uncertainty in vmed (4)
113-118 F6.3 % v1400 [-0.22/0.31] Circular polarization at 1400MHz
from spectral fit to v spectrum
120-124 F5.3 % e_v1400 [0.001/0.02] Uncertainty in v1400
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Note (1): Errors for both the flux density and spectral index are the
formal error on the fit parameters from the covariance matrix.
Note (2): Measured as the average value of polarized intensity and
polarization angle over the channels within ±20MHz of 1400MHz
Note (3): The spectral index of polarized intensity (β) from a
power-law fit to the spectrum of polarized intensity
(Equation 14). Here also the errors are the formal
error on the fit parameter from the covariance matrix.
Note (4): The error is the standard error on the mean derived from
the RMS of the N values over the frequency interval divided by sqrt(N).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 17-Jun-2024