Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz

H. Vedantham 1 E. Koopmans 1 A. De Bruyn 2 S. Wijnholds 3 M. Brentjens 3 F. Abdalla 4 M. Asad 5 G. Bernardi 6 S. Bus 1 E. Chapman 7 B. Ciardi 8 S. Daiboo 1 R. Fernandez 9 A. Ghosh 10 G. Harker 11 V. Jelic 1 H. Jensen 12 S. Kazemi 13 P. Lambropoulos 14, 15 O. Martinez-Rubi 1 G. Mellema 16 M. Mevius 3 A. Offringa 1 V. Pandey 17 A. Patil 18 M. Thomas 19 V. Veligatla 1 S. Yatawatta 3 S. Zaroubi 1 J. Anderson 20 A. Asgekar 3 M. Bell 21 M. Bentum 3 P. Best 22 A. Bonafede 23 F. Breitling 24 J. Broderick 25 M. Bruggen 23 H. Butcher 3 A. Corstanje 26 F. De Gasperin 27 E. De Geus 28 A. Deller 3 S. Duscha 3 J. Eisloffel 29 D. Engels 27 H. Falcke 26 A. Fallows 3 R. Fender 25 C. Ferrari 30 W. Frieswijk 3 M. Garrett 31, 3 J.M. Griessmeier 32, 33 A. Gunst 3 E. Hassall 25 G. Heald 3 M. Hoeft 29 J. Horandel 26 M. Iacobelli 31 E. Juette 34 V. I. Kondratiev 3 M. Kuniyoshi 35 G. Kuper 3 G. Mann 36 S. Markoff 37 R. Mcfadden 38 D. Mckay-Bukowski 39 P. Mckean 38 D. Mulcahy 40 H. Munk 38 A. Nelles 26 M. Norden 3 E. Orru 3 M. Pandey-Pommier 41 R. Pizzo 3 A. Polatidis 3 W. Reich 35 A. Renting 3 H. Rottgering 31 D. Schwarz 42 A. Shulevski 43 O. Smirnov 44 B. W. Stappers 40 M. Steinmetz 45 J. Swinbank 37 Michel Tagger 33 Y. Tang C. Tasse 46 S. Ter Veen 47 S. Thoudam 26 C. Toribio 3 C. Vocks 36 M. W. Wise 37 O. Wucknitz 48 P. Zarka 49
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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 center 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 cross section of visible satellites exceeds 80 m 2 at 800 km height, or 5 m 2 at 400 km height. Currently, our diffuse background spectrum is limited by sidelobe confusion on short baselines (10-15% 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).
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Article dans une revue
Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2015, 450 (3), pp.2291 - 2305. 〈10.1093/mnras/stv746〉
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H. Vedantham, E. Koopmans, A. De Bruyn, S. Wijnholds, M. Brentjens, et al.. Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz. Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP): Policy P - Oxford Open Option A, 2015, 450 (3), pp.2291 - 2305. 〈10.1093/mnras/stv746〉. 〈insu-01182168〉

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