Leakage of diffuse polarized emission into Stokes I caused by the polarized primary beam of the instrument might mimic the spectral structure of the 21-cm signal coming from the epoch of reionization (EoR) making their separation difficult. Therefore, understanding polarimetric performance of the antenna is crucial for a successful detection of the EoR signal. Here, we have calculated the accuracy of the nominal model beam of Low Frequency ARray (LOFAR) in predicting the leakage from Stokes I to Q, U by comparing them with the corresponding leakage of compact sources actually observed in the 3C 295 field. We have found that the model beam has errors of ≤10 per cent on the predicted levels of leakage of ~1 per cent within the field of view, i.e. if the leakage is taken out perfectly using this model the leakage will reduce to 10-3 of the Stokes I flux. If similar levels of accuracy can be obtained in removing leakage from Stokes Q, U to I, we can say, based on the results of our previous paper, that the removal of this leakage using this beam model would ensure that the leakage is well below the expected EoR signal in almost the whole instrumental k-space of the cylindrical power spectrum. We have also shown here that direction-dependent calibration can remove instrumentally polarized compact sources, given an unpolarized sky model, very close to the local noise level.
Bibliographical noteFunding Information:
KMBA, LVEK, and AG 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, MM, SY, and VNP acknowledge support from the European Research Council under grant 399743 (LOFARCORE). SZ acknowledges the support from Lady Davis Foundation andNWO VICI grant. ITI was supported by the Science and Technology Facilities Council [grant numbers ST/F002858/1, ST/I000976/1 and ST/L000652/1].
© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
- Dark ages
- First stars
- Instrumentation: interferometers
- Techniques: interferometric
- Techniques: polarimetric