Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz
Date Issued
2015
Author(s)
Vedantham, H. K.
•
Koopmans, L. V. E.
•
de Bruyn, A. G.
•
Wijnholds, S. J.
•
Brentjens, M.
•
Abdalla, F. B.
•
Asad, K. M. B.
•
•
Bus, S.
•
Chapman, E.
•
Ciardi, B.
•
Daiboo, S.
•
Fernandez, E. R.
•
Ghosh, A.
•
Harker, G.
•
Jelic, V.
•
Jensen, H.
•
Kazemi, S.
•
Lambropoulos, P.
•
Martinez-Rubi, O.
•
Mellema, G.
•
Mevius, M.
•
Offringa, A. R.
•
Pandey, V. N.
•
Patil, A. H.
•
Thomas, R. M.
•
Veligatla, V.
•
Yatawatta, S.
•
Zaroubi, S.
•
Anderson, J.
•
Asgekar, A.
•
Bell, M. E.
•
Bentum, M. J.
•
Best, P.
•
Bonafede, A.
•
Breitling, F.
•
Broderick, J.
•
Brüggen, M.
•
Butcher, H. R.
•
Corstanje, A.
•
•
de Geus, E.
•
Deller, A.
•
Duscha, S.
•
Eislöffel, J.
•
Engels, D.
•
Falcke, H.
•
Fallows, R. A.
•
Fender, R.
•
Ferrari, C.
•
Frieswijk, W.
•
Garrett, M. A.
•
Grießmeier, J.
•
Gunst, A. W.
•
Hassall, T. E.
•
Heald, G.
•
Hoeft, M.
•
Hörandel, J.
•
Iacobelli, M.
•
Juette, E.
•
Kondratiev, V. I.
•
Kuniyoshi, M.
•
Kuper, G.
•
Mann, G.
•
Markoff, S.
•
McFadden, R.
•
McKay-Bukowski, D.
•
McKean, J. P.
•
Mulcahy, D. D.
•
Munk, H.
•
Nelles, A.
•
Norden, M. J.
•
Orru, E.
•
Pandey-Pommier, M.
•
Pizzo, R.
•
Polatidis, A. G.
•
Reich, W.
•
Renting, A.
•
Röttgering, H.
•
Schwarz, D.
•
Shulevski, A.
•
Smirnov, O.
•
Stappers, B. W.
•
Steinmetz, M.
•
Swinbank, J.
•
Tagger, M.
•
Tang, Y.
•
Tasse, C.
•
ter Veen, S.
•
Thoudam, S.
•
Toribio, C.
•
Vocks, C.
•
Wise, M. W.
•
Wucknitz, O.
•
Zarka, P.
Description
We thank Professor Frank Briggs for bringing to our notice an unnecessary approximation to equation ( 7 ) made in an earlier version of the manuscript. We thank the computer group at the Kapteyn Institute for providing the python modules that we used to render Fig. 4 . HKV and LVEK acknowledge the financial support from the European Research Council under ERC-Starting Grant FIRSTLIGHT - 258942. CF acknowledges financial support by the Agence Nationale de la Recherche through grant ANR-09-JCJC-0001-01. LOFAR, the Low Frequency Array designed and constructed by ASTRON, has facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the International LOFAR Telescope (ILT) foundation under a joint scientific policy.
Abstract
We present radio observations of the Moon between 35 and 80 MHz to demonstrate a novel technique of interferometrically measuring large-scale diffuse emission extending far beyond the primary beam (global signal) for the first time. In particular, we show that (i) the Moon appears as a negative-flux source at frequencies 35 < ν < 80 MHz since it is `colder' than the diffuse Galactic background it occults, (ii) using the (negative) flux of the lunar disc, we can reconstruct the spectrum of the diffuse Galactic emission with the lunar thermal emission as a reference, and (iii) that reflected RFI (radio-frequency interference) is concentrated at the centre of the lunar disc due to specular nature of reflection, and can be independently measured. Our RFI measurements show that (i) Moon-based Cosmic Dawn experiments must design for an Earth-isolation of better than 80 dB to achieve an RFI temperature <1 mK, (ii) Moon-reflected RFI contributes to a dipole temperature less than 20 mK for Earth-based Cosmic Dawn experiments, (iii) man-made satellite-reflected RFI temperature exceeds 20 mK if the aggregate scattering cross-section of visible satellites exceeds 175 m2 at 800 km height, or 15 m2 at 400 km height. Currently, our diffuse background spectrum is limited by sidelobe confusion on short baselines (10-15 per cent level). Further refinement of our technique may yield constraints on the redshifted global 21 cm signal from Cosmic Dawn (40 > z > 12) and the Epoch of Reionization (12 > z > 5).
Volume
450
Issue
3
Start page
2291
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.450.2291V
Rights
open.access
File(s)![Thumbnail Image]()
Loading...
Name
Vedantham2015.pdf
Size
1.47 MB
Format
Adobe PDF
Checksum (MD5)
810361b6eca7fcd14268c7b6c1b34526