New Limits on Polarized Power Spectra at 126 and 164 MHz: Relevance to
  Epoch of Reionization Measurements
  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. Using the Donald C. Backer Precision Array for
Probing the Epoch of Reionization (PAPER), we present limits on the observed
power spectra of all four Stokes parameters in two frequency bands, centered at
126 MHz ($z=10.3$) and 164 MHz ($z=7.66$) for 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 as in
those works, and show no definitive detection of polarized power. This
non-detection appears to be largely due to the suppression of polarized power
by ionospheric rotation measure fluctuations, which strongly affect Stokes Q
and U. We are able to show that the net effect of polarized leakage is a
negligible contribution at the levels of of the limits reported in Parsons et
al 2014 and Jacobs et al 2014.
