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Sub-arcsecond imaging with the International LOFAR Telescope II. Completion of the LOFAR Long-Baseline Calibrator Survey

Jackson, Neal; Badole, Shruti; Morgan, John; Chhetri, Rajan; Prūsis, Kaspars; Nikolajevs, Atvars; Morabito, Leah; Brentjens, Michiel; Sweijen, Frits; Iacobelli, Marco; Orrù, Emanuela; Sluman, J.; Blaauw, R.; Mulder, H.; van Dijk, P.; Mooney, Sean; Deller, Adam; Moldon, Javier; Callingham, J.R.; Harwood, Jeremy; Hardcastle, Martin; Heald, George; Drabent, Alexander; McKean, J.P.; Asgekar, A.; Avruch, I.M.; Bentum, M.J.; Bonafede, A.; Brouw, W.N.; Brüggen, M.; Butcher, H.R.; Ciardi, B.; Coolen, A.; Corstanje, A.; Damstra, S.; Duscha, S.; Eislöffel, 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.; Jütte, 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,...

Sub-arcsecond imaging with the International LOFAR Telescope II. Completion of the LOFAR Long-Baseline Calibrator Survey Thumbnail


Authors

Neal Jackson

Shruti Badole

John Morgan

Rajan Chhetri

Kaspars Prūsis

Atvars Nikolajevs

Michiel Brentjens

Frits Sweijen

Marco Iacobelli

Emanuela Orrù

J. Sluman

R. Blaauw

H. Mulder

P. van Dijk

Sean Mooney

Adam Deller

Javier Moldon

J.R. Callingham

Jeremy Harwood

Martin Hardcastle

George Heald

Alexander Drabent

J.P. McKean

A. Asgekar

I.M. Avruch

M.J. Bentum

A. Bonafede

W.N. Brouw

M. Brüggen

H.R. Butcher

B. Ciardi

A. Coolen

A. Corstanje

S. Damstra

S. Duscha

J. Eislöffel

H. Falcke

M. Garrett

F. de Gasperin

J.-M. Griessmeier

A.W. Gunst

M.P. van Haarlem

M. Hoeft

A.J. van der Horst

E. Jütte

L.V.E. Koopmans

A. Krankowski

P. Maat

G. Mann

G.K. Miley

A. Nelles

M. Norden

M. Paas

V.N. Pandey

M. Pandey-Pommier

R.F. Pizzo

W. Reich

H. Rothkaehl

A. Rowlinson

M. Ruiter

A. Shulevski

D.J. Schwarz

O. Smirnov

M. Tagger

C. Vocks

R.J. van Weeren

R. Wijers

O. Wucknitz

P. Zarka

J.A. Zensus

P. Zucca



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.

Citation

Jackson, N., Badole, S., Morgan, J., Chhetri, R., Prūsis, K., Nikolajevs, A., …Zucca, P. (2022). Sub-arcsecond imaging with the International LOFAR Telescope II. Completion of the LOFAR Long-Baseline Calibrator Survey. Astronomy & Astrophysics, 658, Article A2. https://doi.org/10.1051/0004-6361/202140756

Journal Article Type Article
Acceptance Date Apr 29, 2021
Online Publication Date May 27, 2021
Publication Date 2022-02
Deposit Date Jun 29, 2021
Publicly Available Date Mar 29, 2024
Journal Astronomy & Astrophysics
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 658
Article Number A2
DOI https://doi.org/10.1051/0004-6361/202140756

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Copyright Statement
Reproduced with permission, © ESO.





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