The LOFAR ling baseline snapshot calibrator survey

J. Moldon, A.T. Deller, O. Wucknitz, N. Jackson, A. Drabent, T. Carozzi, J. Conway, Marinus Jan Bentum, G. Bernardi, P. Best, A.W. Gunst

Research output: Contribution to journalArticleAcademicpeer-review

3 Citations (Scopus)
15 Downloads (Pure)

Abstract

Aims: An efficient means of locating calibrator sources for international LOw Frequency ARray (LOFAR) is developed and used to determine the average density of usable calibrator sources on the sky for subarcsecond observations at 140 MHz. Methods We used the multi-beaming capability of LOFAR to conduct a fast and computationally inexpensive survey with the full international LOFAR array. Sources were preselected on the basis of 325 MHz arcminute-scale flux density using existing catalogues. By observing 30 different sources in each of the 12 sets of pointings per hour, we were able to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators. Results: More than 40% of the observed sources are detected on multiple baselines between international stations and 86 are classified as satisfactory calibrators. We show that a flat low-frequency spectrum (from 74 to 325 MHz) is the best predictor of compactness at 140 MHz. We extrapolate from our sample to show that the sky density of calibrators that are sufficiently bright to calibrate dispersive and non-dispersive delays for the international LOFAR using existing methods is 1.0 per square degree. Conclusions: The observed density of satisfactory delay calibrator sources means that observations with international LOFAR should be possible at virtually any point in the sky provided that a fast and efficient search, using the methodology described here, is conducted prior to the observation to identify the best calibrator.
Original languageUndefined
Pages (from-to)1-13
Number of pages13
JournalAstronomy & astrophysics
Volume574
Issue numberA73
DOIs
Publication statusPublished - Feb 2015

Keywords

  • EWI-26185
  • IR-96713
  • METIS-312687

Cite this

Moldon, J., Deller, A. T., Wucknitz, O., Jackson, N., Drabent, A., Carozzi, T., ... Gunst, A. W. (2015). The LOFAR ling baseline snapshot calibrator survey. Astronomy & astrophysics, 574(A73), 1-13. https://doi.org/10.1051/0004-6361/201425042
Moldon, J. ; Deller, A.T. ; Wucknitz, O. ; Jackson, N. ; Drabent, A. ; Carozzi, T. ; Conway, J. ; Bentum, Marinus Jan ; Bernardi, G. ; Best, P. ; Gunst, A.W. / The LOFAR ling baseline snapshot calibrator survey. In: Astronomy & astrophysics. 2015 ; Vol. 574, No. A73. pp. 1-13.
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Moldon, J, Deller, AT, Wucknitz, O, Jackson, N, Drabent, A, Carozzi, T, Conway, J, Bentum, MJ, Bernardi, G, Best, P & Gunst, AW 2015, 'The LOFAR ling baseline snapshot calibrator survey' Astronomy & astrophysics, vol. 574, no. A73, pp. 1-13. https://doi.org/10.1051/0004-6361/201425042

The LOFAR ling baseline snapshot calibrator survey. / Moldon, J.; Deller, A.T.; Wucknitz, O.; Jackson, N.; Drabent, A.; Carozzi, T.; Conway, J.; Bentum, Marinus Jan; Bernardi, G.; Best, P.; Gunst, A.W.

In: Astronomy & astrophysics, Vol. 574, No. A73, 02.2015, p. 1-13.

Research output: Contribution to journalArticleAcademicpeer-review

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T1 - The LOFAR ling baseline snapshot calibrator survey

AU - Moldon, J.

AU - Deller, A.T.

AU - Wucknitz, O.

AU - Jackson, N.

AU - Drabent, A.

AU - Carozzi, T.

AU - Conway, J.

AU - Bentum, Marinus Jan

AU - Bernardi, G.

AU - Best, P.

AU - Gunst, A.W.

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Y1 - 2015/2

N2 - Aims: An efficient means of locating calibrator sources for international LOw Frequency ARray (LOFAR) is developed and used to determine the average density of usable calibrator sources on the sky for subarcsecond observations at 140 MHz. Methods We used the multi-beaming capability of LOFAR to conduct a fast and computationally inexpensive survey with the full international LOFAR array. Sources were preselected on the basis of 325 MHz arcminute-scale flux density using existing catalogues. By observing 30 different sources in each of the 12 sets of pointings per hour, we were able to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators. Results: More than 40% of the observed sources are detected on multiple baselines between international stations and 86 are classified as satisfactory calibrators. We show that a flat low-frequency spectrum (from 74 to 325 MHz) is the best predictor of compactness at 140 MHz. We extrapolate from our sample to show that the sky density of calibrators that are sufficiently bright to calibrate dispersive and non-dispersive delays for the international LOFAR using existing methods is 1.0 per square degree. Conclusions: The observed density of satisfactory delay calibrator sources means that observations with international LOFAR should be possible at virtually any point in the sky provided that a fast and efficient search, using the methodology described here, is conducted prior to the observation to identify the best calibrator.

AB - Aims: An efficient means of locating calibrator sources for international LOw Frequency ARray (LOFAR) is developed and used to determine the average density of usable calibrator sources on the sky for subarcsecond observations at 140 MHz. Methods We used the multi-beaming capability of LOFAR to conduct a fast and computationally inexpensive survey with the full international LOFAR array. Sources were preselected on the basis of 325 MHz arcminute-scale flux density using existing catalogues. By observing 30 different sources in each of the 12 sets of pointings per hour, we were able to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators. Results: More than 40% of the observed sources are detected on multiple baselines between international stations and 86 are classified as satisfactory calibrators. We show that a flat low-frequency spectrum (from 74 to 325 MHz) is the best predictor of compactness at 140 MHz. We extrapolate from our sample to show that the sky density of calibrators that are sufficiently bright to calibrate dispersive and non-dispersive delays for the international LOFAR using existing methods is 1.0 per square degree. Conclusions: The observed density of satisfactory delay calibrator sources means that observations with international LOFAR should be possible at virtually any point in the sky provided that a fast and efficient search, using the methodology described here, is conducted prior to the observation to identify the best calibrator.

KW - EWI-26185

KW - IR-96713

KW - METIS-312687

U2 - 10.1051/0004-6361/201425042

DO - 10.1051/0004-6361/201425042

M3 - Article

VL - 574

SP - 1

EP - 13

JO - Astronomy & astrophysics

JF - Astronomy & astrophysics

SN - 0004-6361

IS - A73

ER -

Moldon J, Deller AT, Wucknitz O, Jackson N, Drabent A, Carozzi T et al. The LOFAR ling baseline snapshot calibrator survey. Astronomy & astrophysics. 2015 Feb;574(A73):1-13. https://doi.org/10.1051/0004-6361/201425042