The AARTFAAC Cosmic Explorer: observations of the 21-cm power spectrum in the EDGES absorption trough. Issue 3 (9th October 2020)

• Record Type: Journal Article
• Authors: Gehlot, B K; Mertens, F G; Koopmans, L V E; Offringa, A R; Shulevski, A; Mevius, M; Brentjens, M A; Kuiack, M; Pandey, V N; Rowlinson, A; Sardarabadi, A M; Vedantham, H K; Wijers, R A M J; Yatawatta, S; Zaroubi, S
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 499:Issue 3(2020)
• Page Start: 4158
• Page End: 4173
• Publication Date: 2020-10-09
• Subjects: methods: data analysis -- methods: statistical -- techniques: interferometric -- dark ages, reionization, first stars -- diffuse radiation -- radio lines: general; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa3093
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The 21-cm absorption feature reported by the EDGES collaboration is several times stronger than that predicted by traditional astrophysical models. If genuine, a deeper absorption may lead to stronger fluctuations on the 21-cm signal on degree scales (up to 1 K in rms), allowing these fluctuations to be detectable in nearly 50 times shorter integration times compared to previous predictions. We commenced the 'AARTFAAC Cosmic Explorer' (ACE) program, which employs the AARTFAAC wide-field image, to measure or set limits on the power spectrum of the 21-cm fluctuations in the redshift range z = 17.9–18.6 (Δ ν = 72.36–75.09 MHz) corresponding to the deep part of the EDGES absorption feature. Here, we present first results from two LST bins: 23.5–23.75 and 23.75–24.00 h, each with 2 h of data, recorded in 'semi drift-scan' mode. We demonstrate the application of the new ACE data-processing pipeline (adapted from the LOFAR-EoR pipeline) on the AARTFAAC data. We observe that noise estimates from the channel and time-differenced Stokes V visibilities agree with each other. After 2 h of integration and subtraction of bright foregrounds, we obtain 2 σ upper limits on the 21-cm power spectrum of $\Delta _{21}^2 \lt (8139~\textrm {mK})^2$ and $\Delta _{21}^2 \lt (8549~\textrm {mK})^2$ at $k = 0.144~h\, \textrm {cMpc}^{-1}$ for the two LST bins. Incoherently averaging the noise bias-corrected power spectra for the two LST bins yields an upper limit of $\Delta _{21}^2 \lt (7388~\textrm {mK})^2$ at $k = 0.144~h\, \textrm {cMpc}^{-1}$ . These are the deepest upper limits thus far at these redshifts.