LBCS: The LOFAR Long-Baseline Calibrator Survey - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles Astronomy and Astrophysics - A&A Year : 2016

LBCS: The LOFAR Long-Baseline Calibrator Survey

1 School of Physics and Astronomy [Manchester]
2 ASTRON - Netherlands Institute for Radio Astronomy
3 Departament d'Astronomia i Meteorologia [Barcelona]
4 Onsala Space Observatory, Dept. of Radio and Space Science, Chalmers University of Technology
5 Chalmers University of Technology [Göteborg]
6 CAS - ARC Centre of Excellence for Autonomous Systems
7 IRF - Swedish Institute of Space Physics [Uppsala]
8 DPMMS - Department of Pure Mathematics and Mathematical Statistics
9 Department of Astrophysics [Nijmegen]
10 GFZ - GeoForschungsZentrum - Helmholtz-Zentrum Potsdam
11 Newcastle University [Newcastle]
12 JIVE ERIC - Joint Institute for VLBI in Europe
13 University of Hamburg
14 Leiden Observatory [Leiden]
15 AIP - Leibniz-Institut für Astrophysik Potsdam
16 Oxford Astrophysics
17 University of Southampton
18 Kapteyn Astronomical Institute [Groningen]
19 University of Edinburgh
20 Radboud University [Nijmegen]
21 TLS - Thüringer Landessternwarte Tautenburg
22 Hamburger Sternwarte/Hamburg Observatory
23 USN - Unité Scientifique de la Station de Nançay
24 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
25 MPIFR - Max-Planck-Institut für Radioastronomie
26 Astronomisches Institut der Ruhr-Universität Bochum
27 NAOJ - National Astronomical Observatory of Japan
28 HSE - Health Service Executive [Dublin]
29 AAU - Aalborg University [Denmark]
30 CRAL - Centre de Recherche Astrophysique de Lyon
31 AIP - Astrophysikalisches Institut Potsdam
32 Princeton University
33 SRON - SRON Netherlands Institute for Space Research
34 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
L. Morabito
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F. de Gasperin


We outline LBCS (the LOFAR Long-Baseline Calibrator Survey), whose aim is to identify sources suitable for calibrating the highest-resolution observations made with the International LOFAR Telescope, which include baselines >1000 km. Suitable sources must contain significant correlated flux density (50 − 100 mJy) at frequencies around 110–190 MHz on scales of a few hundred milliarcseconds. At least for the 200–300-km international baselines, we find around 1 suitable calibrator source per square degree over a large part of the northern sky, in agreement with previous work. This should allow a randomly selected target to be successfully phase calibrated on the international baselines in over 50% of cases. Products of the survey include calibrator source lists and fringe-rate and delay maps of wide areas – typically a few degrees – around each source. The density of sources with significant correlated flux declines noticeably with baseline length over the range 200–600 km, with good calibrators on the longest baselines appearing only at the rate of 0.5 per square degree. Coherence times decrease from 1–3 minutes on 200-km baselines to about 1 minute on 600-km baselines, suggesting that ionospheric phase variations contain components with scales of a few hundred kilometres. The longest median coherence time, at just over 3 minutes, is seen on the DE609 baseline, which at 227 km is close to being the shortest. We see median coherence times of between 80 and 110 seconds on the four longest baselines (580–600 km), and about 2 minutes for the other baselines. The success of phase transfer from calibrator to target is shown to be influenced by distance, in a manner that suggests a coherence patch at 150-MHz of the order of 1 degree. Although source structures cannot be measured in these observations, we deduce that phase transfer is affected if the calibrator source structure is not known. We give suggestions for calibration strategies and choice of calibrator sources, and describe the access to the online catalogue and data products.
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Dates and versions

insu-01433110 , version 1 (12-01-2017)



N. Jackson, A A Tagore, Javier, Moldon, Adam Deller, E E Varenius, et al.. LBCS: The LOFAR Long-Baseline Calibrator Survey. Astronomy and Astrophysics - A&A, 2016, 595, 14 pp. ⟨10.1051/0004-6361/201629016⟩. ⟨insu-01433110⟩
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