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The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging

Tasse, C.; Shimwell, T.; Hardcastle, M.J.; O'Sullivan, S.P.; van Weeren, R.; Best, P.N.; Bester, L.; Hugo, B.; Smirnov, O.; Sabater, J.; Calistro-Rivera, G.; de Gasperin, F.; Morabito, L.K.; Röttgering, H.; Williams, W.L.; Bonato, M.; Bondi, M.; Botteon, A.; Brüggen, M.; Brunetti, G.; Chyży, K.T.; Garrett, M.A.; Gürkan, G.; Jarvis, M.J.; Kondapally, R.; Mandal, S.; Prandoni, I.; Repetti, A.; Retana-Montenegro, E.; Schwarz, D.J.; Shulevski, A.; Wiaux, Y.

The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging Thumbnail


C. Tasse

T. Shimwell

M.J. Hardcastle

S.P. O'Sullivan

R. van Weeren

P.N. Best

L. Bester

B. Hugo

O. Smirnov

J. Sabater

G. Calistro-Rivera

F. de Gasperin

H. Röttgering

W.L. Williams

M. Bonato

M. Bondi

A. Botteon

M. Brüggen

G. Brunetti

K.T. Chyży

M.A. Garrett

G. Gürkan

M.J. Jarvis

R. Kondapally

S. Mandal

I. Prandoni

A. Repetti

E. Retana-Montenegro

D.J. Schwarz

A. Shulevski

Y. Wiaux


The Low Frequency Array (LOFAR) is an ideal instrument to conduct deep extragalactic surveys. It has a large field of view and is sensitive to large-scale and compact emission. It is, however, very challenging to synthesize thermal noise limited maps at full resolution, mainly because of the complexity of the low-frequency sky and the direction dependent effects (phased array beams and ionosphere). In this first paper of a series, we present a new calibration and imaging pipeline that aims at producing high fidelity, high dynamic range images with LOFAR High Band Antenna data, while being computationally efficient and robust against the absorption of unmodeled radio emission. We apply this calibration and imaging strategy to synthesize deep images of the Boötes and Lockman Hole fields at ∼150 MHz, totaling ∼80 and ∼100 h of integration, respectively, and reaching unprecedented noise levels at these low frequencies of .30 and .23 µJy beam−1 in the inner ∼3 deg2 . This approach is also being used to reduce the LOTSS-wide data for the second data release.


Tasse, C., Shimwell, T., Hardcastle, M., O'Sullivan, S., van Weeren, R., Best, P., …Wiaux, Y. (2021). The LOFAR Two Meter Sky Survey: Deep Fields, I -- Direction-dependent calibration and imaging. Astronomy & Astrophysics, 648, Article A1.

Journal Article Type Article
Acceptance Date Nov 14, 2020
Online Publication Date Apr 7, 2021
Publication Date 2021-04
Deposit Date Jan 11, 2021
Publicly Available Date Apr 19, 2021
Journal Astronomy and astrophysics.
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 648
Article Number A1


Published Journal Article (14.9 Mb)

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Copyright Statement
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (,<br /> which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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