TITLE:
The GMRT EoR experiment: Limits on polarized sky brightness at 150 MHz.
AUTHOR(S):
Ue-Li Pen, Tzu-Ching Chang, Christopher M. Hirata, Jeffrey B. Peterson, Jayanta Roy, Yashwant Gupta, Julia Odegova, Kris Sigurdson.
DATE:
2008 Jul 07 (arXiv, v1, posted); 2008 Jul 07 (MNRAS, submitted); 2009 Feb 18 (revised); 2009 Apr 25 (MNRAS, accepted);
2009 May 04 (arXiv, v2, posted); 2009 Sep 04 (MNRAS, published).
AVAILABILITY:
arXiv 0807.1056 (free);
Wiley InterScience (requires subscription).
PUBLICATION INFORMATION:
Mon. Not. R. Astron. Soc., 399, 181--194, 2009.
ABSTRACT:
The GMRT reionization effort aims to map out the large scale structure
of the Universe during the epoch of reionization (EoR). Removal of
polarized Galactic emission is a difficult part of any 21 cm EoR program,
and we present new upper limits to diffuse polarized foregrounds at 150
MHz. We find no high significance evidence of polarized emission
in our observed field at mid galactic latitude (J2000 08h27m+27).
We find an upper limit on the 2-dimensional
angular power spectrum of diffuse polarized foregrounds
of [l2Cl/2π]1/2<3K in frequency bins of width δν=1 MHz at 300<l<1000.
The 3-dimensional power spectrum of polarized emission, which is most directly
relevant to EoR observations, is
[k3PP(k)/2π2]1/2<2 K
at k⊥>0.03h Mpc-1, k<0.1h Mpc-1. This can be compared to the expected
EoR signal in total intensity of [k3PP(k)/2π2]1/2~10 mK.
We find polarized
structure is substantially weaker than suggested by extrapolation from
higher frequency observations, so the new low upper limits reported here
reduce the anticipated impact of these foregrounds on EoR experiments.
We discuss Faraday beam and depth depolarization models and compare
predictions of these models to our data. We report on a new technique
for polarization calibration using pulsars, as well as a new technique
to remove broadband radio frequency interference. Our data indicate
that, on the edges of the main beam at GMRT, polarization squint creates
~3% leakage of unpolarized power into polarized maps at zero
rotation measure. Ionospheric rotation was largely stable during these
solar minimum night time observations.
ADS BIBLIOGRAPHIC CODE: 2009MNRAS.399..181P
COMMENTS: N/A.