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We present the first limits on the Epoch of Reionization (EoR) 21-cm HI power spectra, in the redshift range $z=7.9-10.6$, using the Low-Frequency Array (LOFAR) High-Band Antenna (HBA). In total 13,h of data were used from observations centred on the North Celestial Pole (NCP). After subtraction of the sky model and the noise bias, we detect a non-zero $Delta^2_{rm I} = (56 pm 13 {rm mK})^2$ (1-$sigma$) excess variance and a best 2-$sigma$ upper limit of $Delta^2_{rm 21} < (79.6 {rm mK})^2$ at $k=0.053$$h$cMpc$^{-1}$ in the range $z=$9.6-10.6. The excess variance decreases when optimizing the smoothness of the direction- and frequency-dependent gain calibration, and with increasing the completeness of the sky model. It is likely caused by (i) residual side-lobe noise on calibration baselines, (ii) leverage due to non-linear effects, (iii) noise and ionosphere-induced gain errors, or a combination thereof. Further analyses of the excess variance will be discussed in forthcoming publications.
We report upper-limits on the Epoch of Reionization (EoR) 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights of data ($sim36$ hours of integration) from Phase I of the Hydrogen Epoch of Reionization Array (HERA). The Phase I data show evid
We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). Three hours of observati
A new upper limit on the 21-cm signal power spectrum at a redshift of $z approx 9.1$ is presented, based on 141 hours of data obtained with the Low-Frequency Array (LOFAR). The analysis includes significant improvements in spectrally-smooth gain-cali
Spectral distortions in the cosmic microwave background over the 40--200~MHz band are imprinted by neutral hydrogen in the intergalactic medium prior to the end of reionization. This signal, produced in the redshift range $z = 6-34$ at the rest frame
Hemispherical power asymmetry has emerged as a new challenge to cosmology in early universe. While the cosmic microwave background (CMB) measurements indicated the asymmetry amplitude $A simeq 0.07$ at the CMB scale $k_{rm CMB}simeq 0.0045,{rm Mpc}^{