University of Hertfordshire

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From the same journal

By the same authors

  • L. K. Morabito
  • N. J. Jackson
  • S. Mooney
  • F. Sweijen
  • S. Badole
  • P. Kukreti
  • D. Venkattu
  • C. Groeneveld
  • A. Kappes
  • E. Bonnassieux
  • A. Drabent
  • M. Iacobelli
  • J. H. Croston
  • P. N. Best
  • M. Bondi
  • J. R. Callingham
  • J. E. Conway
  • A. T. Deller
  • J. P. McKean
  • G. K. Miley
  • J. Moldon
  • H. J. A. Röttgering
  • C. Tasse
  • T. W. Shimwell
  • R. J. van Weeren
  • J. M. Anderson
  • A. Asgekar
  • I. M. Avruch
  • I. M. van Bemmel
  • M. J. Bentum
  • A. Bonafede
  • W. N. Brouw
  • H. R. Butcher
  • B. Ciardi
  • A. Corstanje
  • A. Coolen
  • S. Damstra
  • F. de Gasperin
  • S. Duscha
  • J. Eislöffel
  • D. Engels
  • H. Falcke
  • M. A. Garrett
  • J. Griessmeier
  • A. W. Gunst
  • M. P. van Haarlem
  • M. Hoeft
  • A. J. van der Horst
  • E. Jütte
  • M. Kadler
  • L. V. E. Koopmans
  • A. Krankowski
  • G. Mann
  • A. Nelles
  • J. B. R. Oonk
  • E. Orru
  • H. Paas
  • V. N. Pandey
  • R. F. Pizzo
  • M. Pandey-Pommier
  • W. Reich
  • H. Rothkaehl
  • M. Ruiter
  • D. J. Schwarz
  • A. Shulevski
  • M. Soida
  • M. Tagger
  • C. Vocks
  • R. A. M. J. Wijers
  • S. J. Wijnholds
  • O. Wucknitz
  • P. Zarka
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Original languageEnglish
JournalAstronomy & Astrophysics
DOIs
Publication statusAccepted/In press - 1 Apr 2021

Abstract

The International LOFAR Telescope is an interferometer with stations spread across Europe. With baselines of up to ~2,000 km, LOFAR has the unique capability of achieving sub-arcsecond resolution at frequencies below 200 MHz, although this is technically and logistically challenging. Here we present a calibration strategy that builds on previous high-resolution work with LOFAR. We give an overview of the calibration strategy and discuss the special challenges inherent to enacting high-resolution imaging with LOFAR, and describe the pipeline, which is publicly available, in detail. We demonstrate the calibration strategy by using the pipeline on P205+55, a typical LOFAR Two-metre Sky Survey (LoTSS) pointing. We perform in-field delay calibration, solution referencing to other calibrators, self-calibration, and imaging of example directions of interest in the field. For this specific field and these ionospheric conditions, dispersive delay solutions can be transferred between calibrators up to ~1.5 degrees away, while phase solution transferral works well over 1 degree. We demonstrate a check of the astrometry and flux density scale. Imaging in 17 directions, the restoring beam is typically 0.3" x 0.2" although this varies slightly over the entire 5 square degree field of view. We achieve ~80 to 300 $\mu$Jy/bm image rms noise, which is dependent on the distance from the phase centre; typical values are ~90 $\mu$Jy/bm for the 8 hour observation with 48 MHz of bandwidth. Seventy percent of processed sources are detected, and from this we estimate that we should be able to image ~900 sources per LoTSS pointing. This equates to ~3 million sources in the northern sky, which LoTSS will entirely cover in the next several years. Future optimisation of the calibration strategy for efficient post-processing of LoTSS at high resolution (LoTSS-HR) makes this estimate a lower limit.

Notes

Accepted to a special issue of A&A on sub-arcsecond imaging with LOFAR. 24 pages, 16 figures

ID: 25797194