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The LOFAR Two-metre Sky Survey

Shimwell, T. W. and Hardcastle, M. J. and Tasse, C. and Best, P. N. and Röttgering, H. J. A. and Williams, W. L. and Botteon, A. and Drabent, A. and Mechev, A. and Shulevski, A. and van Weeren, R. J. and Bester, L. and Brüggen, M. and Brunetti, G. and Callingham, J. R. and Chyży, K. T. and Conway, J. E. and Dijkema, T. J. and Duncan, K. and de Gasperin, F. and Hale, C. L. and Haverkorn, M. and Hugo, B. and Jackson, N. and Mevius, M. and Miley, G. K. and Morabito, L. K. and Morganti, R. and Offringa, A. and Oonk, J. B. R. and Rafferty, D. and Sabater, J. and Smith, D. J. B. and Schwarz, D. J. and Smirnov, O. and O’Sullivan, S. P. and Vedantham, H. and White, G. J. and Albert, J. G. and Alegre, L. and Asabere, B. and Bacon, D. J. and Bonafede, A. and Bonnassieux, E. and Brienza, M. and Bilicki, M. and Bonato, M. and Calistro Rivera, G. and Cassano, R. and Cochrane, R. and Croston, J. H. and Cuciti, V. and Dallacasa, D. and Danezi, A. and Dettmar, R. J. and Di Gennaro, G. and Edler, H. W. and Enßlin, T. A. and Emig, K. L. and Franzen, T. M. O. and García-Vergara, C. and Grange, Y. G. and Gürkan, G. and Hajduk, M. and Heald, G. and Heesen, V. and Hoang, D. N. and Hoeft, M. and Horellou, C. and Iacobelli, M. and Jamrozy, M. and Jelić, V. and Kondapally, R. and Kukreti, P. and Kunert-Bajraszewska, M. and Magliocchetti, M. and Mahatma, V. and Małek, K. and Mandal, S. and Massaro, F. and Meyer-Zhao, Z. and Mingo, B. and Mostert, R. I. J. and Nair, D. G. and Nakoneczny, S. J. and Nikiel-Wroczyński, B. and Orrú, E. and Pajdosz-Śmierciak, U. and Pasini, T. and Prandoni, I. and van Piggelen, H. E. and Rajpurohit, K. and Retana-Montenegro, E. and Riseley, C. J. and Rowlinson, A. and Saxena, A. and Schrijvers, C. and Sweijen, F. and Siewert, T. M. and Timmerman, R. and Vaccari, M. and Vink, J. and West, J. L. and Wołowska, A. and Zhang, X. and Zheng, J. (2022) 'The LOFAR Two-metre Sky Survey.', Astronomy & Astrophysics, 659 . A1.

Abstract

In this data release from the ongoing LOw-Frequency ARray (LOFAR) Two-metre Sky Survey we present 120–168 MHz images covering 27% of the northern sky. Our coverage is split into two regions centred at approximately 12h45m +44◦300 and 1h00m +28◦000 and spanning 4178 and 1457 square degrees respectively. The images were derived from 3451 h (7.6 PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4 396 228 radio sources is derived from our total intensity (Stokes I) maps, where the majority of these have never been detected at radio wavelengths before. At 600 resolution, our full bandwidth Stokes I continuum maps with a central frequency of 144 MHz have: a median rms sensitivity of 83 µJy beam−1 ; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.200; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8 mJy beam−1 . By creating three 16 MHz bandwidth images across the band we are able to measure the in-band spectral index of many sources, albeit with an error on the derived spectral index of >±0.2 which is a consequence of our flux-density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes V) 2000 resolution 120–168 MHz continuum images have a median rms sensitivity of 95 µJy beam−1 , and we estimate a Stokes I to Stokes V leakage of 0.056%. Our linear polarisation (Stokes Q and Stokes U) image cubes consist of 480 × 97.6 kHz wide planes and have a median rms sensitivity per plane of 10.8 mJy beam−1 at 40 and 2.2 mJy beam−1 at 2000; we estimate the Stokes I to Stokes Q/U leakage to be approximately 0.2%. Here we characterise and publicly release our Stokes I, Q, U and V images in addition to the calibrated uv-data to facilitate the thorough scientific exploitation of this unique dataset.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1051/0004-6361/202142484
Publisher statement:Reproduced with permission, © ESO.
Date accepted:23 December 2021
Date deposited:14 June 2022
Date of first online publication:25 February 2022
Date first made open access:14 June 2022

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