J/A+A/658/A2 LOFAR Long-Baseline Calibrator Survey. II. (Jackson+, 2022)
Sub-arcsecond imaging with the International LOFAR Telescope.
II. Completion of the LOFAR Long-Baseline Calibrator Survey.
Jackson N., Badole S., Morgan J., Chhetri R., Prusis K., Nikolajevs A.,
Morabito L., Brentjens M., Sweijen F., Iacobelli M., Orru E., J.S.,
Blaauw R., Mulder H., van Dijk P., Mooney S., Deller A., Moldon J.,
Callingham J.R., Harwood J., Hardcastle M., Heald G., Drabent A.,
McKean J.P., Asgekar A., Avruch I.M., Bentum M.J., Bonafede A., Brouw W.N.,
Brueggen M., Butcher H.R., Ciardi B., Coolen A., Corstanje A., Damstra S.,
Duscha S., Eisloeel J., Falcke H., Garrett M., de Gasperin F.,
Griessmeier J.-M., Gunst A.W., van Haarlem M.P., Hoeft M.,
van der Horst A.J., Juette E., Koopmans L.V.E., Krankowski A., Maat P.,
Mann G., Miley G.K., Nelles A., Norden M., Paas M., Pandey V.N.,
Pandey-Pommier M., Pizzo R.F., Reich W., Rothkaehl H., Rowlinson A.,
Ruiter M., Shulevski A., Schwarz D.J., Smirnov O., Tagger M., Vocks C.,
van Weeren R.J., Wijers R., Wucknitz O., Zarka P., Zensus J.A., Zucca P.
<Astron. Astrophys. 658, A2 (2022)>
=2022A&A...658A...2J 2022A&A...658A...2J (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Radio sources ; Radio continuum ; Interferometry
Keywords: instrumentation: interferometers - techniques: interferometric -
surveys - galaxies: active - radio continuum: galaxies -
Abstract:
The Low-Frequency Array (LOFAR) Long-Baseline Calibrator Survey (LBCS)
was conducted between 2014 and 2019 in order to provide a set of
calibrators for the LOFAR array. Here we present the complete survey,
for which a preliminary analysis was published in 2016 using 20% of
the survey data. The final catalogue consists of 30007 observations of
24713 sources in the northern sky, selected for a combination of
bright low-frequency radio flux density and flat spectral index using
existing surveys (WENSS, VLSS and MSSS). Approximately 1 calibrator
per square degree is identified by the detection of compact flux, for
declinations north of 30° and a considerably lower density south
of this point. The catalogue contains indicators of degree of
correlated flux on baselines between the Dutch core and each of the
international stations for all of the observations. Use of the VLBA
calibrator list, together with statistical arguments by comparison
with flux densities from lower-resolution catalogues, allow us to
establish a rough flux density scale for the LBCS observations, so
that LBCS statistics can be used to estimate compact fluxes, on scales
between 300mas and 2-arcseconds, for sources observed in the survey.
Description:
Coherence measurements are presented for 24700 northern-sky radio
sources using the LOFAR International Telescope. Measurements concern
correlated flux density on baselines between the LOFAR Dutch core and
13 international stations with baselines ranging from 250km to 1890km.
They are presented in the form of 'P', 'S' and 'X' designations for
well-detected, slightly-detected, and non-detected sources at each
baseline length, based on scatter in fringe fits, and also in terms of
signal-to-noise ratios. The minimum detectable correlated flux is
about 130mJy at the observing frequency of 140MHz.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
lbcsall.dat 116 30007 Positions and coherence measurements
lbcscons.dat 116 24713 Positions and coherence measurements, with multiple
observations of the same source consolidated and
with the best coherence measurement reported
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See also:
VIII/62 : The Westerbork Northern Sky Survey (Leiden, 1998)
J/A+A/658/A4 : LOFAR imaging of Arp299 at 150MHz (Ramirez-Olivencia, 2022)
J/A+A/658/A5 : Hercules A LOFAR and JVLA images (Timmerman+, 2022)
J/A+A/658/A6 : 3C293 high and low resolution maps (Kukreti+, 2022)
J/A+A/658/A8 : Resolved jet of 3C 273 at 150 MHz (Harwood+, 2022)
J/A+A/658/A10 : 3C295 LOFAR, MERLIN and VLA images (Bonnassieux+, 2022)
Byte-by-byte Description of file: lbcsall.dat lbcscons.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- LBCS LBCS survey designation, observation number
10- 11 I2 h RAh Right ascension (J2000.0) from the WENSS survey
13- 14 I2 min RAm Right ascension (J2000.0) from the WENSS survey
16- 20 F5.2 s RAs Right ascension (J2000.0) from the WENSS survey
22 A1 --- DE- Declination sign (J2000.0) from the WENSS
survey
23- 24 I2 deg DEd Declination (J2000.0) from the WENSS survey
26- 27 I2 arcmin DEm Declination (J2000.0) from the WENSS survey
29- 32 F4.1 arcsec DEs Declination (J2000.0) from the WENSS survey
35- 44 A10 "date" Obs.date Observation date (YYYY-MM-DD)
47- 54 A8 "h:m:s" Obs.time Observation time UT (hh:mm:ss)
57- 69 A13 --- CorrF Correlated flux on telescopes from fringe
fit (1)
72 A1 --- Qual Quality flag (2)
75- 87 A13 --- CorrS Correlated flux on telescopes from S:N (3)
90- 92 I3 --- Qual2 Quality flag 2 (4)
96-105 F10.6 deg RAdeg Right ascension (J2000.0) from the WENSS survey
108-116 F9.6 deg DEdeg Declination (J2000.0) from the WENSS survey
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Note (1): The 13 characters in this field refer to the 13 LOFAR stations, in
order:
DE601 Effelsberg, DE602 Unterweilenbach, DE603 Tautenberg,
DE604 Potsdam, DE605 Juelich, FR606 Nancay, SE607 Onsala, UK608 Chilbolton,
DE609 Norderstedt, PL610 Borowiec, PL611 Lazy, PL612 Baldy, IE613 Birr.
For each station a designation of P, S or X is given.
P represents a clear detection of correlated flux to this station from
phase and delay scatter in the fringe fit. S represents a low signal
to noise detection and X represents a weak or non-detection.
Calibrators should ideally be chosen which have P or S on required
baseline lengths, which range from 250 kmfor DE605 to 1890km for IE613.
Note (2): Quality flag based on observations as follows:
O = good observation
A = anomalous amplitudes but otherwise good
M = failed observation, few channels
X = failed observation, few time steps
Z = more than half the data is flagged
Note (3): The 13 characters in this field refer to the 13 LOFAR stations, in
order:
DE601 Effelsberg, DE602 Unterweilenbach, DE603 Tautenberg, DE604 Potsdam,
DE605 Juelich, FR606 Nancay, SE607 Onsala, UK608 Chilbolton, DE609
Norderstedt, PL610 Borowiec, PL611 Lazy, PL612 Baldy, IE613 Birr.
For each station a number from 0-9 is given, where 0 represents less than
about 150mJy of correlated flux and 9 represents >370mJy at 140MHz on
the baseline concerned.
Note (4): Quality flag based on the proportion of sources in the batch which
were detected during the observation.
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Acknowledgements:
Neal Jackson, neal.jackson(at)manchester.ac.uk
References:
Morabito et al., Paper I 2022A&A...658A...1M 2022A&A...658A...1M
Sweijen et al., Paper III 2022A&A...658A...3S 2022A&A...658A...3S
Ramirez-Olivencia et al., Paper IV 2022A&A...658A...4R 2022A&A...658A...4R, Cat, J/A+A/658/A4
Timmerman et al., Paper V 2022A&A...658A...5T 2022A&A...658A...5T, Cat, J/A+A/658/A5
Kukreti et al., Paper VI 2022A&A...658A...6K 2022A&A...658A...6K, Cat, J/A+A/658/A6
Badole et al., Paper VII 2022A&A...658A...7B 2022A&A...658A...7B
Harwood et al., Paper VIII 2022A&A...658A...8H 2022A&A...658A...8H, Cat, J/A+A/658/A8
Groeneveld et al., Paper IX 2022A&A...658A...9G 2022A&A...658A...9G
Bonnassieux et al., Paper X 2022A&A...658A..10B 2022A&A...658A..10B, Cat. J/A+A/658/A10
(End) Neal Jackson [Manchester Univ.], Patricia Vannier [CDS] 04-May-2021