The brightness and spatial distributions of terrestrial radio sources
Abstract
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
Cite
@article{arxiv.1307.5580,
title = {The brightness and spatial distributions of terrestrial radio sources},
author = {A. R. Offringa and A. G. de Bruyn and S. Zaroubi and L. V. E. Koopmans and S. J. Wijnholds and F. B. Abdalla and W. N. Brouw and B. Ciardi and I. T. Iliev and G. J. A. Harker and G. Mellema and G. Bernardi and P. Zarka and A. Ghosh and A. Alexov and J. Anderson and A. Asgekar and I. M. Avruch and R. Beck and M. E. Bell and M. R. Bell and M. J. Bentum and P. Best and L. Bîrzan and F. Breitling and J. Broderick and M. Brüggen and H. R. Butcher and F. de Gasperin and E. de Geus and M. de Vos and S. Duscha and J. Eislöffel and R. A. Fallows and C. Ferrari and W. Frieswijk and M. A. Garrett and J. Grießmeier and T. E. Hassall and A. Horneffer and M. Iacobelli and E. Juette and A. Karastergiou and W. Klijn and V. I. Kondratiev and M. Kuniyoshi and G. Kuper and J. van Leeuwen and M. Loose and P. Maat and G. Macario and G. Mann and J. P. McKean and H. Meulman and M. J. Norden and E. Orru and H. Paas and M. Pandey-Pommier and R. Pizzo and A. G. Polatidis and D. Rafferty and W. Reich and R. van Nieuwpoort and H. Röttgering and A. M. M. Scaife and J. Sluman and O. Smirnov and C. Sobey and M. Tagger and Y. Tang and C. Tasse and S. ter Veen and C. Toribio and R. Vermeulen and C. Vocks and R. J. van Weeren and M. W. Wise and O. Wucknitz},
journal= {arXiv preprint arXiv:1307.5580},
year = {2013}
}
Comments
Accepted for publication in MNRAS