The HERA-19 Commissioning Array: Direction Dependent Effects
Creators: name: Kohn, Saul A.
name: Aguirre, James E.
name: La Plante, Paul
name: Billings, Tashalee S.
name: Chichura, Paul M.
name: Fortino, Austin F.
name: Igarashi, Amy S.
name: Benefo, Roshan K.
name: Gallardo, Samavarti
name: Martinot, Zachary E.
name: Nunhokee, Chuneeta D.
name: Kern, Nicholas S.
name: Bull, Philip
name: Liu, Adrian
name: Alexander, Paul
name: Ali, Zaki S.
name: Beardsley, Adam P.
name: Bernardi, Gianni
name: Bowman, Judd D.
name: Bradley, Richard F.
name: Carilli, Chris L.
name: Cheng, Carina
name: DeBoer, David R.
name: Acedo, Eloy de Lera
name: Dillon, Joshua S.
name: Ewall-Wice, Aaron
name: Fadana, Gcobisa
name: Fagnoni, Nicolas
name: Fritz, Randall
name: Furlanetto, Steven R.
name: Glendenning, Brian
name: Greig, Bradley
name: Grobbelaar, Jasper
name: Hazelton, Bryna J.
name: Hewitt, Jacqueline N.
name: Hickish, Jack
name: Jacobs, Daniel C.
name: Julius, Austin
name: Kariseb, MacCalvin
name: Kolopanis, Matthew
name: Lekalake, Telalo
name: Loots, Anita
name: MacMahon, David
name: Malan, Lourence
name: Malgas, Cresshim
name: Maree, Matthys
name: Mathison, Nathan
name: Matsetela, Eunice
name: Mesinger, Andrei
name: Morales, Miguel F.
name: Neben, Abraham R.
name: Nikolic, Bojan
name: Parsons, Aaron R.
name: Patra, Nipanjana
name: Pieterse, Samantha
name: Pober, Jonathan C.
name: Razavi-Ghods, Nima
name: Ringuette, Jon
name: Robnett, James
name: Rosie, Kathryn
name: Sell, Raddwine
name: Smith, Craig
name: Syce, Angelo
name: Tegmark, Max
name: Thyagarajan, Nithyanandan
name: Williams, Peter K. G.
name: Zheng, Haoxuan
Publisher: name: arXiv
Year: 2018
Subjects: subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Foreground power dominates the measurements of interferometers that seek a statistical detection of highly-redshifted HI emission from the Epoch of Reionization (EoR). The chromaticity of the instrument creates a boundary in the Fourier transform of frequency (proportional to $k_\parallel$) between spectrally smooth emission, characteristic of the strong synchrotron foreground (the "wedge"), and the spectrally structured emission from HI in the EoR (the "EoR window"). Faraday rotation can inject spectral structure into otherwise smooth polarized foreground emission, which through instrument effects or miscalibration could possibly pollute the EoR window. Using data from the HERA 19-element commissioning array, we investigate the polarization response of this new instrument in the power spectrum domain. We perform a simple image-based calibration based on the unpolarized diffuse emission of the Global Sky Model, and show that it achieves qualitative redundancy between the nominally-redundant baselines of the array and reasonable amplitude accuracy. We construct power spectra of all fully polarized coherencies in all pseudo-Stokes parameters. We compare to simulations based on an unpolarized diffuse sky model and detailed electromagnetic simulations of the dish and feed, confirming that in Stokes I, the calibration does not add significant spectral structure beyond the expected level. Further, this calibration is stable over the 8 days of observations considered. Excess power is seen in the power spectra of the linear polarization Stokes parameters which is not easily attributable to leakage via the primary beam, and results from some combination of residual calibration errors and actual polarized emission. Stokes V is found to be highly discrepant from the expectation of zero power, strongly pointing to the need for more accurate polarized calibration.
description: 21 pages, 12 figures, submitted to ApJ