A Method to Extract the Angular Power Spectrum of the Epoch of
  Reionization from Low-Frequency Radio Interferometers
  The redshifted 21cm signal of neutral hydrogen from the epoch of reionization
(EoR) is extremely weak and its first detection is therefore expected to be
statistical with first-generation low-frequency radio interferometers. In this
letter we propose a method to extract the angular power spectrum of EoR from
the visibility correlation coefficients p_{ij}(u,v), instead of the
visibilities V_{ij}(u,v) measured directly by radio interferometers in
conventional algorithm. The visibility correlation coefficients are defined as
p_{ij}(u,v)=V_{ij}(u,v)/\sqrt{|V_{ii}||V_{jj}|} by introducing the
auto-correlation terms V_{ii} and V_{jj} such that the angular power spectrum
C_{\ell} can be obtained through C_{\ell}=4pi^2T_0^2<|p_{ij}(u,v)|^2>,
independently of the primary beams of antennas. This also removes partially the
influence of receiver gains in the measurement of C_{\ell} because the
amplitudes of the gains cancel each other out in the statistical average
operation of <|p_{ij}(u,v)|^2>.We use the average system temperature T_0 as a
calibrator of C_{\ell}, which is dominated by the Milky Way and extragalactic
sources in our interested frequency range below 200 MHz. Finally we demonstrate
the feasibility of the novel method using the simulated sky maps as targets and
the 21 CentiMeter Array (21CMA) as interferometer.
