THE PRECISION ARRAY FOR PROBING THE EPOCH OF RE-IONIZATION: EIGHT STATION RESULTS

Abstract

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