Limits on Polarized Leakage for the PAPER Epoch of Reionization Measurements at 126 and 164 MHz

Polarized foreground emission is a potential contaminant of attempts to measure the fluctuation power spectrum of highly redshifted 21 cm Hi emission from the epoch of reionization, yet observational constraints on the level of polarized emission are poor. Using the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER), we present the first limits on the power spectra of all four Stokes parameters in two frequency bands, centered at 126 MHz (z = 10.3) and 164 MHz (z = 7.66). This data comes from from a three-month observing campaign of a 32-antenna deployment, for which unpolarized power spectrum results have been reported at z = 7.7 (Parsons et al. 2014) and 7.5 < z < 10.5 (Jacobs et al. 2014). The power spectra in this paper are processed in the same way, and show no definitive detection of polarized power. The limits are sufficiently low that we are able to show that the excess unpolarized power reported in those works is not due to leakage of Faraday-rotated polarized emission. Building upon the Moore et al. (2013) simulations of polarized point sources, we further argue that our upper limits and previous observations imply that the mean polarization fraction of point sources at these frequencies is ∼ 2×10 −3 , roughly an order of magnitude lower than that observed for point sources at 1.4 GHz.