The Precision Array for Probing the Epoch of Reionization: 8 Station Results

TL;DR

This paper reports on the development and deployment of the PAPER array to detect 21cm signals from the early Universe, including system performance, sky mapping, and power spectrum analysis, advancing the quest to observe reionization.

Contribution

It presents new results from 8-station deployments of PAPER, including system characterization, all-sky mapping, and power spectrum measurements relevant to Epoch of Reionization studies.

Findings

All-sky map reaches 80 mJy sensitivity at 154 MHz.

Power spectra dominated by point sources, with galactic emission contributions.

Thermal noise level of 310 mK at $\,\ell=100$

Abstract

We are developing the Precision Array for Probing the Epoch of Reionization (PAPER) to detect 21cm emission from the early Universe, when the first stars and galaxies were forming. We describe the overall experiment strategy and architecture and summarize two PAPER deployments: a 4-antenna array in the low-RFI environment of Western Australia and an 8-antenna array at our prototyping site in Green Bank, WV. From these activities we report on system performance, including primary beam model verification, dependence of system gain on ambient temperature, measurements of receiver and overall system temperatures, and characterization of the RFI environment at each deployment site. We present an all-sky map synthesized between 139 MHz and 174 MHz using data from both arrays that reaches down to 80 mJy (4.9 K, for a beam size of 2.15e-5 steradians at 154 MHz), with a 10 mJy (620 mK) thermal noise level that indicates what would be achievable with better foreground subtraction. We calculate angular power spectra ($C_\ell$) in a cold patch and determine them to be dominated by point sources, but with contributions from galactic synchrotron emission at lower radio frequencies and angular wavemodes. Although the cosmic variance of foregrounds dominates errors in these power spectra, we measure a thermal noise level of 310 mK at $\ell=100$ for a 1.46-MHz band centered at 164.5 MHz. This sensitivity level is approximately three orders of magnitude in temperature above the level of the fluctuations in 21cm emission associated with reionization.