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.
Techniques: interferometric
Methods: data analysis
Instrumentation: interferometers
Dark ages, reionization, first stars
Författare
S. Yatawatta
Rijksuniversiteit Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
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
Mount Stromlo Observatory
Rijksuniversiteit Groningen
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
Rijksuniversiteit Groningen
Harvard-Smithsonian Center for Astrophysics
B. Ciardi
Max-Planck-Gesellschaft
S. Daiboo
Rijksuniversiteit Groningen
G. Harker
University of Colorado
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-Gesellschaft
I. M. Avruch
Netherlands Institute for Space Research (SRON)
Rijksuniversiteit Groningen
Fabien Batejat
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
M. E. Bell
The University of Sydney
University of Southampton
M. R. Bell
Max-Planck-Gesellschaft
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-Gemeinschaft
R. H. van de Brink
Netherlands Institute for Radio Astronomy (ASTRON)
J. W. Broderick
University of Southampton
M. Brüggen
Universität Hamburg
Jacobs University Bremen
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
Netherlands Institute for Radio Astronomy (ASTRON)
Centre national de la recherche scientifique (CNRS)
A. W. Gunst
Netherlands Institute for Radio Astronomy (ASTRON)
T. E. Hassall
University of Southampton
University of Manchester
J. W. T. Hessels
Universiteit Van Amsterdam
Netherlands Institute for Radio Astronomy (ASTRON)
M. Hoeft
Thüringer Landessternwarte Tautenburg
M. Iacobelli
Universiteit Leiden
E. Juette
Ruhr-Universität Bochum
A. Karastergiou
University of Oxford
V. I. Kondratiev
Astro Space Center of Lebedev Physical Institute
Netherlands Institute for Radio Astronomy (ASTRON)
M. Kramer
Max-Planck-Gesellschaft
University of Manchester
M. Kuniyoshi
Max-Planck-Gesellschaft
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-Gemeinschaft
J. P. McKean
Netherlands Institute for Radio Astronomy (ASTRON)
M. Mevius
Rijksuniversiteit Groningen
Netherlands Institute for Radio Astronomy (ASTRON)
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
Observatoire de Lyon
Universiteit Leiden
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
A. G. Polatidis
Netherlands Institute for Radio Astronomy (ASTRON)
W. Reich
Max-Planck-Gesellschaft
H. Rottgering
Universiteit Leiden
J. Sluman
Netherlands Institute for Radio Astronomy (ASTRON)
O. Smirnov
Rhodes University
B. Stappers
University of Manchester
M. Steinmetz
Leibniz-Gemeinschaft
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
Netherlands Institute for Radio Astronomy (ASTRON)
Harvard-Smithsonian Center for Astrophysics
Universiteit Leiden
M. Wise
Netherlands Institute for Radio Astronomy (ASTRON)
O. Wucknitz
Argelander-Institut für Astronomie
Max-Planck-Gesellschaft
P. Zarka
Observatoire de Paris-Meudon
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 550 A136Ämneskategorier (SSIF 2011)
Astronomi, astrofysik och kosmologi
DOI
10.1051/0004-6361/201220874