Beamforming Errors in Murchison Widefield Array Phased Array Antennas and their Effects on Epoch of Reionization Science
Abstract
Accurate antenna beam models are critical for radio observations aiming to isolate the redshifted 21 cm spectral line emission from the Dark Ages and the Epoch of Reionization (EOR) and unlock the scientific potential of 21 cm cosmology. Past work has focused on characterizing mean antenna beam models using either satellite signals or astronomical sources as calibrators, but antennatoantenna variation due to imperfect instrumentation has remained unexplored. We characterize this variation for the Murchison Widefield Array (MWA) through laboratory measurements and simulations, finding typical deviations of the order of ±10%20% near the edges of the main lobe and in the sidelobes. We consider the ramifications of these results for image and power spectrumbased science. In particular, we simulate visibilities measured by a 100 m baseline and find that using an otherwise perfect foreground model, unmodeled beamforming errors severely limit foreground subtraction accuracy within the region of Fourier space contaminated by foreground emission (the “wedge”). This region likely contains much of the cosmological signal, and accessing it will require measurement of perantenna beam patterns. However, unmodeled beamforming errors do not contaminate the Fourier space region expected to be free of foreground contamination (the “EOR window”), showing that foreground avoidance remains a viable strategy.
 Publication:

The Astrophysical Journal
 Pub Date:
 March 2016
 DOI:
 10.3847/0004637X/820/1/44
 arXiv:
 arXiv:1602.05249
 Bibcode:
 2016ApJ...820...44N
 Keywords:

 cosmology: observations;
 dark ages;
 reionization;
 first stars;
 instrumentation: interferometers;
 methods: statistical;
 techniques: interferometric;
 Astrophysics  Instrumentation and Methods for Astrophysics;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 Accepted to ApJ