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## Upper Limits on the 21cm Epoch of Reionization Power Spectrum from One Night with LOFAR

Patil, AH; Yatawatta, S; Koopmans, LVE; de Bruyn, AG; Brentjens, MA; Zaroubi, S; Asad, KMB; ... Wijnholds, SJ; + view all (2017) Upper Limits on the 21cm Epoch of Reionization Power Spectrum from One Night with LOFAR. The Astrophysical Journal , 838 (1) , Article 65. 10.3847/1538-4357/aa63e7.

## Abstract

We present the first limits on the Epoch of Reionization 21 cm H i power spectra, in the redshift range z = 7.9–10.6, using the Low-Frequency Array (LOFAR) High-Band Antenna (HBA). In total, 13.0 hr of data were used from observations centered on the North Celestial Pole. After subtraction of the sky model and the noise bias, we detect a non-zero ${{\rm{\Delta }}}_{{\rm{I}}}^{2}={(56\pm 13\mathrm{mK})}^{2}$ (1-σ) excess variance and a best 2-σ upper limit of ${{\rm{\Delta }}}_{21}^{2}\lt {(79.6\mathrm{mK})}^{2}$ at k = 0.053 h cMpc−1 in the range z = 9.6–10.6. The excess variance decreases when optimizing the smoothness of the direction- and frequency-dependent gain calibration, and with increasing the completeness of the sky model. It is likely caused by (i) residual side-lobe noise on calibration baselines, (ii) leverage due to nonlinear effects, (iii) noise and ionosphere-induced gain errors, or a combination thereof. Further analyses of the excess variance will be discussed in forthcoming publications.

Type: Article Upper Limits on the 21cm Epoch of Reionization Power Spectrum from One Night with LOFAR An open access version is available from UCL Discovery 10.3847/1538-4357/aa63e7 https://doi.org/10.3847/1538-4357/aa63e7 English This is the published version of record. For information on re-use, please refer to the publisher’s terms and conditions. dark ages, reionization, first stars UCLUCL > Provost and Vice Provost Offices > UCL BEAMSUCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical SciencesUCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy https://discovery.ucl.ac.uk/id/eprint/1556637