Initial deep LOFAR observations of epoch of reionization windows I. The north celestial pole
Artikel i vetenskaplig tidskrift, 2013

Aims. The aim of the LOFAR epoch of reionization (EoR) project is to detect the spectral fluctuations of the redshifted HI 21 cm signal. This signal is weaker by several orders of magnitude than the astrophysical foreground signals and hence, in order to achieve this, very long integrations, accurate calibration for stations and ionosphere and reliable foreground removal are essential. Methods. One of the prospective observing windows for the LOFAR EoR project will be centered at the north celestial pole (NCP). We present results from observations of the NCP window using the LOFAR highband antenna (HBA) array in the frequency range 115 MHz to 163 MHz. The data were obtained in April 2011 during the commissioning phase of LOFAR. We used baselines up to about 30 km. The data was processed using a dedicated processing pipeline which is an enhanced version of the standard LOFAR processing pipeline. Results. With about 3 nights, of 6 h each, effective integration we have achieved a noise level of about 100 mu Jy/PSF in the NCP window. Close to the NCP, the noise level increases to about 180 mu Jy/PSF, mainly due to additional contamination from unsubtracted nearby sources. We estimate that in our best night, we have reached a noise level only a factor of 1.4 above the thermal limit set by the noise from our Galaxy and the receivers. Our continuum images are several times deeper than have been achieved previously using the WSRT and GMRT arrays. We derive an analytical explanation for the excess noise that we believe to be mainly due to sources at large angular separation from the NCP. We present some details of the data processing challenges and how we solved them. Conclusions. Although many LOFAR stations were, at the time of the observations, in a still poorly calibrated state we have seen no artefacts in our images which would prevent us from producing deeper images in much longer integrations on the NCP window which are about to commence. The limitations present in our current results are mainly due to sidelobe noise from the large number of distant sources, as well as errors related to station beam variations and rapid ionospheric phase fluctuations acting on bright sources. We are confident that we can improve our results with refined processing.

Methods: data analysis

Instrumentation: interferometers

Dark ages, reionization, first stars

Techniques: interferometric

Författare

S. Yatawatta

Netherlands Institute for Radio Astronomy (ASTRON)

Rijksuniversiteit Groningen

A. G. de Bruyn

Rijksuniversiteit Groningen

Netherlands Institute for Radio Astronomy (ASTRON)

M. A. Brentjens

Netherlands Institute for Radio Astronomy (ASTRON)

P. Labropoulos

Netherlands Institute for Radio Astronomy (ASTRON)

V. N. Pandey

Netherlands Institute for Radio Astronomy (ASTRON)

S. Kazemi

Rijksuniversiteit Groningen

S. Zaroubi

Rijksuniversiteit Groningen

L. V. E. Koopmans

Rijksuniversiteit Groningen

A. R. Offringa

Rijksuniversiteit Groningen

Mount Stromlo Observatory

V. Jelic

Rijksuniversiteit Groningen

O. M. Rubi

Rijksuniversiteit Groningen

V. Veligatla

Rijksuniversiteit Groningen

S. J. Wijnholds

Netherlands Institute for Radio Astronomy (ASTRON)

W. N. Brouw

Netherlands Institute for Radio Astronomy (ASTRON)

G. Bernardi

Harvard-Smithsonian Center for Astrophysics

Rijksuniversiteit Groningen

B. Ciardi

Max-Planck-Institut für Astrophysik

S. Daiboo

Rijksuniversiteit Groningen

G. Harker

University of Colorado at Boulder

G. Mellema

Stockholms universitet

J. Schaye

Universiteit Leiden

R Thomas

Rijksuniversiteit Groningen

H. Vedantham

Rijksuniversiteit Groningen

E. Chapman

University College London (UCL)

F. B. Abdalla

University College London (UCL)

A. Alexov

Space Telescope Science Institute (STScI)

J. Anderson

Max-Planck-Institut für Astrophysik

I. M. Avruch

Netherlands Institute for Space Research (SRON)

Rijksuniversiteit Groningen

Fabien Batejat

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

M. E. Bell

University of Southampton

The University of Sydney

M. R. Bell

Max-Planck-Institut für Astrophysik

M. Bentum

Netherlands Institute for Radio Astronomy (ASTRON)

P. Best

Royal Observatory

A. Bonafede

Jacobs University Bremen

J. Bregman

Netherlands Institute for Radio Astronomy (ASTRON)

F. Breitling

Leibniz-Institut Für Astrophysik Potsdam

R. H. van de Brink

Netherlands Institute for Radio Astronomy (ASTRON)

J. W. Broderick

University of Southampton

M. Brüggen

Jacobs University Bremen

Universität Hamburg

John Conway

Chalmers, Rymd- och geovetenskap, Onsala rymdobservatorium

F. De Gasperin

Universität Hamburg

E. de Geus

Netherlands Institute for Radio Astronomy (ASTRON)

S. Duscha

Netherlands Institute for Radio Astronomy (ASTRON)

H. Falcke

Radboud Universiteit

R. A. Fallows

Netherlands Institute for Radio Astronomy (ASTRON)

C. Ferrari

Université Nice Sophia Antipolis (UNS)

W. Frieswijk

Netherlands Institute for Radio Astronomy (ASTRON)

M. A. Garrett

Universiteit Leiden

Netherlands Institute for Radio Astronomy (ASTRON)

J. M. Griessmeier

Centre national de la recherche scientifique (CNRS)

Netherlands Institute for Radio Astronomy (ASTRON)

A. W. Gunst

Netherlands Institute for Radio Astronomy (ASTRON)

T. E. Hassall

University of Manchester

University of Southampton

J. W. T. Hessels

Netherlands Institute for Radio Astronomy (ASTRON)

Universiteit Van Amsterdam

M. Hoeft

Thüringer Landessternwarte Tautenburg

M. Iacobelli

Universiteit Leiden

E. Juette

Ruhr-Universität Bochum

A. Karastergiou

University of Oxford

V. I. Kondratiev

Netherlands Institute for Radio Astronomy (ASTRON)

Astro Space Center of Lebedev Physical Institute

M. Kramer

University of Manchester

Max-Planck-Institut für Astrophysik

M. Kuniyoshi

Max-Planck-Institut für Astrophysik

G. Kuper

Netherlands Institute for Radio Astronomy (ASTRON)

J. van Leeuwen

Netherlands Institute for Radio Astronomy (ASTRON)

Universiteit Van Amsterdam

P. Maat

Netherlands Institute for Radio Astronomy (ASTRON)

G. Mann

Leibniz-Institut Für Astrophysik Potsdam

J. P. McKean

Netherlands Institute for Radio Astronomy (ASTRON)

M. Mevius

Netherlands Institute for Radio Astronomy (ASTRON)

Rijksuniversiteit Groningen

J. D. Mol

Netherlands Institute for Radio Astronomy (ASTRON)

H. Munk

Netherlands Institute for Radio Astronomy (ASTRON)

R. Nijboer

Netherlands Institute for Radio Astronomy (ASTRON)

J. E. Noordam

Netherlands Institute for Radio Astronomy (ASTRON)

M. J. Norden

Netherlands Institute for Radio Astronomy (ASTRON)

E. Orru

Radboud Universiteit

Netherlands Institute for Radio Astronomy (ASTRON)

H. Paas

Rijksuniversiteit Groningen

M. Pandey-Pommier

Universiteit Leiden

Observatoire de Lyon

R. Pizzo

Netherlands Institute for Radio Astronomy (ASTRON)

A. G. Polatidis

Netherlands Institute for Radio Astronomy (ASTRON)

W. Reich

Max-Planck-Institut für Astrophysik

H. Rottgering

Universiteit Leiden

J. Sluman

Netherlands Institute for Radio Astronomy (ASTRON)

O. Smirnov

Rhodes University

B. Stappers

University of Manchester

M. Steinmetz

Leibniz-Institut Für Astrophysik Potsdam

M. Tagger

Centre national de la recherche scientifique (CNRS)

Y. Tang

Netherlands Institute for Radio Astronomy (ASTRON)

C. Tasse

Observatoire de Paris-Meudon

S. ter Veen

Radboud Universiteit

R. Vermeulen

Netherlands Institute for Radio Astronomy (ASTRON)

R. J. van Weeren

Harvard-Smithsonian Center for Astrophysics

Netherlands Institute for Radio Astronomy (ASTRON)

Universiteit Leiden

M. Wise

Netherlands Institute for Radio Astronomy (ASTRON)

O. Wucknitz

Argelander-Institut für Astronomie

Max-Planck-Institut für Astrophysik

P. Zarka

Observatoire de Paris-Meudon

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 550 A136

Ämneskategorier

Astronomi, astrofysik och kosmologi

DOI

10.1051/0004-6361/201220874

Mer information

Senast uppdaterat

2021-07-08