Polarization leakage in epoch of reionization windows - I. Low Frequency Array observations of the 3C196 field
Date Issued
2015
Author(s)
Asad, K. M. B.
•
Koopmans, L. V. E.
•
Jelić, V.
•
Pandey, V. N.
•
Ghosh, A.
•
Abdalla, F. B.
•
BERNARDI, GIANNI
•
Brentjens, M. A.
•
de Bruyn, A. G.
•
Bus, S.
•
Ciardi, B.
•
Chapman, E.
•
Daiboo, S.
•
Fernandez, E. R.
•
Harker, G.
•
Iliev, I. T.
•
Jensen, H.
•
Martinez-Rubi, O.
•
Mellema, G.
•
Mevius, M.
•
Offringa, A. R.
•
Patil, A. H.
•
Schaye, J.
•
Thomas, R. M.
•
van der Tol, S.
•
Vedantham, H. K.
•
Yatawatta, S.
•
Zaroubi, S.
Description
We thank the anonymous reviewer for his/her useful comments. KMBA, LVEK, AG and HKV acknowledge the financial support from the European Research Council under ERC-Starting Grant FIRSTLIGHT – 258942. VJ acknowledges the financial support from The Netherlands Organization for Scientific Research (NWO) under VENI grant – 639.041.336. AGdB, SBY and VNP acknowledge support from the European Research Council under grant 399743 (LOFARCORE). AHP and SZ acknowledge the support from Lady Davis Foundation and NWO VICI grant. GH acknowledges funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement no. 327999. ITI was supported by the Science and Technology Facilities Council [grant numbers ST/F002858/1, ST/I000976/1 and ST/L000652/1]. In addition, KMBA would like to thank George Heald and Cyril Tasse for useful suggestions.
Abstract
Detection of the 21-cm signal coming from the epoch of reionization (EoR) is challenging especially because, even after removing the foregrounds, the residual Stokes I maps contain leakage from polarized emission that can mimic the signal. Here, we discuss the instrumental polarization of Low Frequency Array (LOFAR) and present realistic simulations of the leakages between Stokes parameters. From the LOFAR observations of polarized emission in the 3C196 field, we have quantified the level of polarization leakage caused by the nominal model beam of LOFAR, and compared it with the EoR signal using power spectrum analysis. We found that at 134-166 MHz, within the central 4° of the field the (Q, U) → I leakage power is lower than the EoR signal at k < 0.3 Mpc-1. The leakage was found to be localized around a Faraday depth of 0, and the rms of the leakage as a fraction of the rms of the polarized emission was shown to vary between 0.2 and 0.3 per cent, 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 power spectrum above the point spread function (PSF)-induced wedge and below k∥ ̃ 0.5 Mpc-1, and the window extended up to k∥ ̃ 1 Mpc-1 at all k⊥ when 70 per cent of the leakage had been removed. These LOFAR results show that even a modest polarimetric calibration over a field of view of ≲ 4° in the future arrays like Square Kilometre Array will ensure that the polarization leakage remains well below the expected EoR signal at the scales of 0.02-1 Mpc-1.
Volume
451
Issue
4
Start page
3709
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.451.3709A
Rights
open.access