17 research outputs found
Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64
The Epoch of Reionization (EoR) is an uncharted era in our Universe's history
during which the birth of the first stars and galaxies led to the ionization of
neutral hydrogen in the intergalactic medium. There are many experiments
investigating the EoR by tracing the 21cm line of neutral hydrogen. Because
this signal is very faint and difficult to isolate, it is crucial to develop
analysis techniques that maximize sensitivity and suppress contaminants in
data. It is also imperative to understand the trade-offs between different
analysis methods and their effects on power spectrum estimates. Specifically,
with a statistical power spectrum detection in HERA's foreseeable future, it
has become increasingly important to understand how certain analysis choices
can lead to the loss of the EoR signal. In this paper, we focus on signal loss
associated with power spectrum estimation. We describe the origin of this loss
using both toy models and data taken by the 64-element configuration of the
Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER).
In particular, we highlight how detailed investigations of signal loss have led
to a revised, higher 21cm power spectrum upper limit from PAPER-64.
Additionally, we summarize errors associated with power spectrum error
estimation that were previously unaccounted for. We focus on a subset of
PAPER-64 data in this paper; revised power spectrum limits from the PAPER
experiment are presented in a forthcoming paper by Kolopanis et al. (in prep.)
and supersede results from previously published PAPER analyses.Comment: 25 pages, 18 figures, Accepted by Ap
The Correlation Calibration of PAPER-64 data
Observation of redshifted 21-cm signal from the Epoch of Reionization (EoR)
is challenging due to contamination from the bright foreground sources that
exceed the signal by several orders of magnitude. The removal of this very high
foreground relies on accurate calibration to keep the intrinsic property of the
foreground with frequency. Commonly employed calibration techniques for these
experiments are the sky model-based and the redundant baseline-based
calibration approaches. However, the sky model-based and redundant
baseline-based calibration methods could suffer from sky-modeling error and
array redundancy imperfection issues, respectively. In this work, we introduce
the hybrid correlation calibration ("CorrCal") scheme, which aims to bridge the
gap between redundant and sky-based calibration by relaxing redundancy of the
array and including sky information into the calibration formalisms. We
demonstrate the slight improvement of power spectra, about deviation at
the bin right on the horizon limit of the foreground wedge-like structure,
relative to the power spectra before the implementation of "CorrCal" to the
data from the Precision Array for Probing the Epoch of Reionization (PAPER)
experiment, which was otherwise calibrated using redundant baseline
calibration. This small improvement of the foreground power spectra around the
wedge limit could be suggestive of reduced spectral structure in the data after
"CorrCal" calibration, which lays the foundation for future improvement of the
calibration algorithm and implementation method