Characterizing Signal Loss in the 21 cm Reionization Power Spectrum: A Revised Study of PAPER-64

Abstract

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 21 cm 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 21 cm 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.

Improved upper limits on the 21 cm signal power spectrum of neutral hydrogen at z ≈ 9.1 from LOFAR

“…Paciga et al 2013) and power spectra estimation (e.g. Cheng et al 2018;Kolopanis et al 2019). To ensure limited signal loss or bias of the 21-cm signal power spectra, a number of checks were performed at various steps in the processing pipeline.…”

Absolute Calibration Strategies for the Hydrogen Epoch of Reionization Array and Their Impact on the 21 cm Power Spectrum

“…This is one measure of the uncertainty on the power spectra due to noise, but also represents the theoretical amplitude of the power spectra in the limit that they are noise dominated (as opposed to signal or systematic dominated). This is given in Cheng et al (2018) as…”

“…One of the only direct probes of the IGM throughout the entirety of Cosmic Dawn is neutral hydrogen's 21 cm transition, which at redshifts of z ∼ 10 appears in the low-frequency radio band around 150 MHz. Over the past decade, first-generation 21 cm EoR experiments like the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER; Parsons et al 2014;Jacobs et al 2015;Cheng et al 2018;Kolopanis et al 2019), the Murchison Widefield Array (MWA; Tingay et al 2013;Dillon et al 2014;Beardsley et al 2016;Barry et al 2019b;Li et al 2019), the Low Frequency Array (LOFAR; van Haarlem et al 2013;Patil et al 2017;Gehlot et al 2019), the Giant Metre Wave Radio Telescope (GMRT; Paciga et al 2013), and the Long Wavelength Array (LWA; Eastwood et al 2019) have set increasing stringent limits on the Cosmic Dawn 21 cm power spectrum. Meanwhile, global signal experiments have placed constraints on the 21 cm monopole (Bernardi et al 2016;Singh et al 2017), with a reported first detection of the signal at Cosmic Dawn from the Experiment to Detect the Global EoR Signature (EDGES; Bowman et al 2018).…”

Mitigating Internal Instrument Coupling for 21 cm Cosmology. I. Temporal and Spectral Modeling in Simulations

“…We now turn our attention to another systematic we refer to as antenna cross coupling, which acts to couple one antenna's voltage stream with another antenna's voltage stream before reaching the correlation stage. Note that our model for cross coupling is different than "capacitive crosstalk" created by the electric field of two parallel signal chains interacting with each other within cabling, receivers, and analogue-to-digital conversion (ADC) units, which is a common systematic for radio interferometers (Parsons & Backer 2009;Zheng et al 2014;Ali et al 2015;Patil et al 2017;Cheng et al 2018). There are well established hardware solutions for suppressing crosstalk, such as phase switching (Chaudhari et al 2017).…”