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