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  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., Pr¯usis, K., Nikolajevs, A., et al. (2022). Sub-arcsecond imaging with the International LOFAR Telescope - II. Completion of the LOFAR Long-Baseline Calibrator Survey. Astronomy and Astrophysics, 658: A2. doi:10.1051/0004-6361/202140756.

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Jackson, N., Author
Badole, S., Author
Morgan, J., Author
Chhetri, R., Author
Pr¯usis, K., Author
Nikolajevs, A., Author
Morabito, L., Author
Brentjens, M., Author
Sweijen, F., Author
Iacobelli, M., Author
Orrù, E., Author
Sluman, J., Author
Blaauw, R., Author
Mulder, H., Author
van Dijk, P., Author
Mooney, S., Author
Deller, A., Author
Moldon, J., Author
Callingham, J. R., Author
Harwood, J., Author
Hardcastle, M., AuthorHeald, G., AuthorDrabent, A., AuthorMcKean, J. P., AuthorAsgekar, A., AuthorAvruch, I. M., AuthorBentum, M. J., AuthorBonafede, A., AuthorBrouw, W. N., AuthorBrüggen, M., AuthorButcher, H. R., AuthorCiardi, B.1, Author              Coolen, A., AuthorCorstanje, A., AuthorDamstra, S., AuthorDuscha, S., AuthorEislöffel, J., AuthorFalcke, H., AuthorGarrett, M., Authorde Gasperin, F., AuthorGriessmeier, J.-M., AuthorGunst, A. W., Authorvan Haarlem, M. P., AuthorHoeft, M., Authorvan der Horst, A. J., AuthorJütte, E., AuthorKoopmans, L. V. E., AuthorKrankowski, A., AuthorMaat, P., AuthorMann, G., AuthorMiley, G. K., AuthorNelles, A., AuthorNorden, M., AuthorPaas, M., AuthorPandey, V. N., AuthorPandey-Pommier, M., AuthorPizzo, R. F., AuthorReich, W., AuthorRothkaehl, H., AuthorRowlinson, A., AuthorRuiter, M., AuthorShulevski, A., AuthorSchwarz, D. J., AuthorSmirnov, O., AuthorTagger, M., AuthorVocks, C., Authorvan Weeren, R. J., AuthorWijers, R., AuthorWucknitz, O., AuthorZarka, P., AuthorZensus, J. A., AuthorZucca, P., Author more..
Affiliations:
1Computational Structure Formation, MPI for Astrophysics, Max Planck Society, ou_2205642              

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 Abstract: The Low-Frequency Array (LOFAR) Long-Baseline Calibrator Survey (LBCS) was conducted between 2014 and 2019 in order to obtain a set of suitable calibrators for the LOFAR array. In this paper, we present the complete survey, building on the preliminary analysis published in 2016 which covered approximately half the survey area. The final catalogue consists of 30 006 observations of 24 713 sources in the northern sky, selected for a combination of high low-frequency radio flux density and flat spectral index using existing surveys (WENSS, NVSS, VLSS, and MSSS). Approximately one calibrator per square degree, suitable for calibration of ≥200 km baselines is identified by the detection of compact flux density, for declinations north of 30° and away from the Galactic plane, with a considerably lower density south of this point due to relative difficulty in selecting flat-spectrum candidate sources in this area of the sky. The catalogue contains indicators of degree of correlated flux on baselines between the Dutch core and each of the international stations, involving a maximum baseline length of nearly 2000 km, 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 flux densities on scales between 300 mas and 2′′, for sources observed in the survey. The survey is used to estimate the phase coherence time of the ionosphere for the LOFAR international baselines, with median phase coherence times of about 2 min varying by a few tens of percent between theshortest and longest baselines. The LBCS can be used to assess the structures of point sources in lower-resolution surveys, with significant reductions in the degree of coherence in these sources on scales between 2′′ and 300 mas. The LBCS survey sources show a greater incidence of compact flux density in quasars than in radio galaxies, consistent with unified schemes of radio sources. Comparison with samples of sources from interplanetary scintillation (IPS) studies with the Murchison Widefield Array shows consistent patterns of detection of compact structure in sources observed both interferometrically with LOFAR and using IPS.

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Language(s): eng - English
 Dates: 2022-01-25
 Publication Status: Published online
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.1051/0004-6361/202140756
 Degree: -

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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
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Publ. Info: France : EDP Sciences S A
Pages: - Volume / Issue: 658 Sequence Number: A2 Start / End Page: - Identifier: ISSN: 1432-0746
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1