The brightness and spatial distributions of terrestrial radio sources

A. R. Offringa (1) , A. G. de Bruyn (2) , S. Zaroubi (2) , L. V. E. Koopmans (2) , S. J. Wijnholds (3) , F. B. Abdalla (4) , B. Ciardi (5) , W. N. Brouw (3) , I. T. Iliev (6) , G. J. A. Harker (7) , G. Mellema (8) , G. Bernardi (9) , P. Zarka (10) , A. Ghosh (2) , A. Alexov (11) , A. Asgekar (3) , J. Anderson (12) , I. M. Avruch (13) , R. Beck (12) , M. R. Bell (5) , M. J. Bentum (3) , P. Best (14) , L. Bîrzan (15) , F. Breitling (16) , J. Broderick (17) , M. Brüggen (18) , H. R. Butcher (3) , F. de Gasperin (18) , E. de Geus (3) , M. de Vos (3) , S. Duscha (3) , J. Eislöffel (19) , W. Frieswijk (3) , R. A. Fallows (3) , C. Ferrari (20) , M. A. Garrett (15) , Jean-Mathias Griessmeier (21) , T. E. Hassall (17) , A. Horneffer (12) , M. Iacobelli (15) , E. Juette (22) , J. P. Mckean (3) , A. Karastergiou (23) , W. Klijn (3) , V. I. Kondratiev (3) , M. Kuniyoshi (12) , G. Kuper (3) , J. van Leeuwen (24) , M. Loose (3) , P. Maat (3) , G. Macario (20) , G. Mann (16) , H. Meulman (3) , M. J. Norden (3) , E. Orru (3) , H. Paas (25) , M. Pandey-Pommier (26) , R. Pizzo (3) , A. G. Polatidis (3) , D. Rafferty (15) , W. Reich (12) , R. van Nieuwpoort (3) , H. Röttgering (15) , A. M. M. Scaife (17) , J. Sluman (3) , O. Smirnov (27) , C. Sobey (12) , Michel Tagger (21) , Y. Tang (3) , C. Tasse (10) , S. ter Veen (28) , C. Toribio (3) , R. Vermeulen (3) , C. Vocks (16) , R. J. van Weeren (9) , M. W. Wise (29) , O. Wucknitz (30)

1 RSAA - Research School of Astronomy and Astrophysics [Canberra]
2 Kapteyn Astronomical Institute [Groningen]
3 Netherlands Institute for Radio Astronomy ( ASTRON )
4 UCL - University College of London [London]
5 MPA - Max-Planck-Institut für Astrophysik
6 University of Sussex
7 CASA - Center for Astrophysics and Space Astronomy [Boulder]
8 AlbaNova University Center
9 CfA - Harvard-Smithsonian Center for Astrophysics
10 LESIA - Laboratoire d'études spatiales et d'instrumentation en astrophysique
11 STSci - Space Telescope Science Institute
12 MPIFR - Max-Planck-Institut für Radioastronomie
13 SRON - SRON Netherlands Institute for Space Research
14 University of Edinburgh
15 Leiden Observatory [Leiden]
16 AIP - Leibniz-Institut für Astrophysik Potsdam
17 School of Physics and Astronomy [Southampton]
18 UHH - Universität Hamburg
19 TLS - Thüringer Landessternwarte Tautenburg
20 LAGRANGE - Joseph Louis LAGRANGE
21 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
22 Ruhr-Universität Bochum [Bochum]
23 Oxford Astrophysics
24 UvA - University of Amsterdam [Amsterdam]
25 Center for Information Technology CIT
26 CRAL - Centre de Recherche Astrophysique de Lyon
27 Department of Physics-Electronics
28 IMAPP - Institute for Mathematics, Astrophysics and Particle Physics
29 AI PANNEKOEK - Astronomical Institute Anton Pannekoek
30 AlfA - Argelander-Institut für Astronomie

Faint undetected sources of radio-frequency interference (RFI) might become visible in long radio observations when they are consistently present over time. Thereby, they might obstruct the detection of the weak astronomical signals of interest. This issue is especially important for Epoch of Reionisation (EoR) projects that try to detect the faint redshifted HI signals from the time of the earliest structures in the Universe. We explore the RFI situation at 30-163 MHz by studying brightness histograms of visibility data observed with LOFAR, similar to radio-source-count analyses that are used in cosmology. An empirical RFI distribution model is derived that allows the simulation of RFI in radio observations. The brightness histograms show an RFI distribution that follows a power-law distribution with an estimated exponent around -1.5. With several assumptions, this can be explained with a uniform distribution of terrestrial radio sources whose radiation follows existing propagation models. Extrapolation of the power law implies that the current LOFAR EoR observations should be severely RFI limited if the strength of RFI sources remains strong after time integration. This is in contrast with actual observations, which almost reach the thermal noise and are thought not to be limited by RFI. Therefore, we conclude that it is unlikely that there are undetected RFI sources that will become visible in long observations. Consequently, there is no indication that RFI will prevent an EoR detection with LOFAR.

Keywords: reionisation; atmospheric effects – instrumentation: interferometers – methods: observational – techniques: interferometric – radio continuum: general – dark ages; first stars

Domains: Geophysics [physics.geo-ph]; Atmospheric and Oceanic Physics [physics.ao-ph]

A. R. Offringa, A. G. de Bruyn, S. Zaroubi, L. V. E. Koopmans, S. J. Wijnholds, et al.. The brightness and spatial distributions of terrestrial radio sources. Monthly Notices of the Royal Astronomical Society, 2013, 435, pp.584-596. ⟨10.1093/mnras/stt1337⟩. ⟨insu-01291191⟩