Lunar occultation of the diffuse radio sky: LOFAR measurements between 35 and 80 MHz
Number of Authors: 95
2015 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 450, no 3, 2291-2305 p.Article in journal (Refereed) Published
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 < nu < 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 m(2) at 800 km height, or 15 m(2) 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).
Place, publisher, year, edition, pages
2015. Vol. 450, no 3, 2291-2305 p.
methods: observational, techniques: interferometric, Moon, dark ages, reionization, first stars
Astronomy, Astrophysics and Cosmology
IdentifiersURN: urn:nbn:se:su:diva-119138DOI: 10.1093/mnras/stv746ISI: 000356339300005OAI: oai:DiVA.org:su-119138DiVA: diva2:843758