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 34 E. Juette 35 V. I. Kondratiev 3 M. Kuniyoshi 36 G. Kuper 3 G. Mann 37 S. Markoff 38 R. Mcfadden 39 D. Mckay-Bukowski 40 P. Mckean 39 D. Mulcahy 41 H. Munk 39 A. Nelles 26 M. Norden 3 E. Orru 3 M. Pandey-Pommier 42 R. Pizzo 3 A. Polatidis 3 W. Reich 36 A. Renting 3 H. Rottgering 31 D. Schwarz 43 A. Shulevski 44 O. Smirnov 45 B. W. Stappers 41 M. Steinmetz 46 J. Swinbank 38 Michel Tagger 33 Y. Tang 47 C. Tasse 48 S. Ter Veen 49 S. Thoudam 26 C. Toribio 3 C. Vocks 37 M. W. Wise 38 O. Wucknitz 50 P. Zarka 51
5 MSE - Mécanique des Solides et des Endommagements
LaMCoS - Laboratoire de Mécanique des Contacts et des Structures [Villeurbanne]
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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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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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Soumis le : mardi 16 mai 2017 - 15:12:45
Dernière modification le : samedi 20 mai 2017 - 01:07:47

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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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