2015A&A...574A..73M

Query : 2015A&A...574A..73M

2015A&A...574A..73M - Astronomy and Astrophysics, volume 574A73-73 (2015/2-1)

The LOFAR long baseline snapshot calibrator survey.

MOLDON J., DELLER A.T., WUCKNITZ O., JACKSON N., DRABENT A., CAROZZI T., CONWAY J., KAPINSKA A.D., McKEAN J.P., MORABITO L., VARENIUS E., ZARKA P., ANDERSON J., ASGEKAR A., AVRUCH I.M., BELL M.E., BENTUM M.J., BERNARDI G., BEST P., BIRZAN L., BREGMAN J., BREITLING F., BRODERICK J.W., BRUEGGEN M., BUTCHER H.R., CARBONE D., CIARDI B., DE GASPERIN F., DE GEUS E., DUSCHA S., EISLOFFEL J., ENGELS D., FALCKE H., FALLOWS R.A., FENDER R., FERRARI C., GARRETT M.A., GRIESSMEIER J., GUNST A.W., HAMAKER J.P., HASSALL T.E., HEALD G., HOEFT M., JUETTE E., KARASTERGIOU A., KONDRATIEV V.I., KRAMER M., KUNIYOSHI M., KUPER G., MAAT P., MANN G., MARKOFF S., McFADDEN R., McKAY-BUKOWSKI D., MORGANTI R., MUNK H., NORDEN M.J., OFFRINGA A.R., ORRU E., PAAS H., PANDEY-POMMIER M., PIZZO R., POLATIDIS A.G., REICH W., ROETTGERING H., ROWLINSON A., SCAIFE A.M.M., SCHWARZ D., SLUMAN J., SMIRNOV O., STAPPERS B.W., STEINMETZ M., TAGGER M., TANG Y., THOUDAM S., TORIBIO M.C., VERMEULEN R., VOCKS C., VAN WEEREN R.J., WHITE S., WISE M.W., YATAWATTA S. and ZENSUS A.

Abstract (from CDS):

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 140MHz. 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 325MHz 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. 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 325MHz) is the best predictor of compactness at 140MHz. 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. 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.

Abstract Copyright: ∼

Journal keyword(s): instrumentation: high angular resolution - instrumentation: interferometers - methods: observational - techniques: interferometric - techniques: high angular resolution - catalogs

VizieR on-line data: <Available at CDS (J/A+A/574/A73): lofarlb.dat>

Simbad objects: 20

Full paper

View the references in ADS

Number of rows : 20

N	Identifier	Otype	ICRS (J2000) RA	ICRS (J2000) DEC	Mag U	Mag B	Mag V	Mag R	Sp type	#ref 1850 - 2026	#notes
1	6C 021803+354230	BLL	02 21 05.4920852208	+35 56 13.848581904		20.0	20.0	19.60	~	603	3
2	3C 196	Sy1	08 13 36.0561170112	+48 13 02.644966020		18.36	17.79		~	578	2
3	M 82	AGN	09 55 52.430	+69 40 46.93	9.61	9.30	8.41		~	6156	6
4	3C 295	Sy1	14 11 20.6	+52 12 09		22.34	20.80	18.54	~	1021	4
5	M 13	GlC	16 41 41.634	+36 27 40.75			5.8		~	2291	0
6	7C 1721+5859	Bla	17 22 36.72659456	+58 56 22.2606924		19.47	19.44	19.00	~	72	1
7	NAME Galactic Center	reg	17 45 39.60213	-29 00 22.0000					~	16269	0
8	6C 182501+575039	QSO	18 25 41.5982799192	+57 53 05.962185024					~	20	1
9	2C 1569	Bla	18 29 31.7809732968	+48 44 46.160168892		17.05	16.81	16.860	~	713	1
10	3C 395	Bla	19 02 55.93889653	+31 59 41.7016439			17.5		~	281	2
11	NVSS J192722+712540	Rad	19 27 22.08	+71 25 38.5					~	3	1
12	4C 73.18	BLL	19 27 48.4947009120	+73 58 01.572558816			16.06	15.11	~	562	2
13	NVSS J192830+703838	Rad	19 28 30.448	+70 38 37.66					~	4	1
14	NVSS J193020+712735	Rad	19 30 19.375	+71 27 37.02					~	3	1
15	NVSS J193119+721022	Rad	19 31 18.24	+72 10 23.8					~	3	1
16	NVSS J193447+734513	Rad	19 34 47.17	+73 45 14.0					~	4	1
17	NVSS J193651+713447	Rad	19 36 50.93	+71 34 47.6					~	3	1
18	NVSS J193840+724257	Rad	19 38 40.18	+72 42 58.2					~	3	1
19	NVSS J194123+710046	Rad	19 41 23.254	+71 00 46.76					~	3	1
20	4C 72.27	Sy2	19 45 16.5998907150	+72 47 58.171546942					~	13	1

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