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Polarization leakage in Epoch of Reionization windows: I. LOFAR observations of the 3C196 field | Khan M. B. Asad
; Léon V. E. Koopmans
; Vibor Jelić
; V. N. Pandey
; Abhik Ghosh
; F. B. Abdalla
; G. Bernardi
; M. A. Brentjens
; A. G. de Bruyn
; S. Bus
; B. Ciardi
; E. Chapman
; S. Daiboo
; E. R. Fernandez
; G. Harker
; I. T. Iliev
; H. Jensen
; O. Martinez-Rubi
; G. Mellema
; M. Mevius
; A. R. Offringa
; A. H. Patil
; J. Schaye
; R. M. Thomas
; S. van der Tol
; H. K. Vedantham
; S. Yatawatta
; S. Zaroubi
; | Date: |
5 Mar 2015 | Abstract: | Detection of the cosmological 21-cm signal coming from the epoch of
reionization (EoR) is challenging in the presence of astrophysical foregrounds
and direction (in)dependent systematic errors of the instrument. Even after
removing the foregrounds, the residual Stokes I maps contain, in addition to
the system noise, the polarized foreground leaked from Stokes Q, U due to
systematic and random errors which can mimic the EoR signal. Here we discuss
the systematic errors, especially the primary beam, of LOFAR and present
realistic simulations of the leakages caused by them. We made a Stokes Q, U sky
model of the Galactic diffuse emission based on the LOFAR observations of the
3C196 field, simulated the full-Stokes visibilities that would be produced by
LOFAR in the presence of its nominal model beam, created RM-cubes and the
cylindrically and spherically averaged 3D power spectra (PS), and compared them
with the PS of a simulated EoR signal. From the spherical PS, we found that at
134-166 MHz, within the central 4 deg of the field the (Q, U ) to I leakage
power is lower than the EoR signal at k < 0.3 /Mpc. The leakage was found to be
localized around a Faraday depth of 0, and in the cylindrical PS, the rms of
the leakage as a fraction of the rms of the polarized emission was shown to
vary between 0.2-0.3%, both of which could be utilized in the removal of
leakage. Moreover, we could define an ’EoR window’ in terms of the polarization
leakage in the cylindrical PS above the PSF-induced wedge and below
$k_parallelsim 0.5$ /Mpc, and the window extended up to $k_parallelsim 1$
/Mpc at all $k_perp$ when 70% of the leakage had been removed. These LOFAR
results show that even a modest polarimetric calibration over a field of view
of $lesssim$ 4 deg in the future arrays like SKA will ensure that the
polarization leakage remains well below the expected EoR signal at the scales
of 0.02-1 /Mpc. | Source: | arXiv, 1503.1644 | Services: | Forum | Review | PDF | Favorites |
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