The Hydrogen Epoch of Reionization Array Dish I: Beam Pattern Measurements and Science Implications

TL;DR

This paper characterizes the angular response of HERA's dish, providing crucial measurements and simulations that inform its sensitivity and foreground handling for detecting the Epoch of Reionization's 21 cm signal.

Contribution

It presents the first detailed measurement and analysis of HERA's dish beam pattern, linking it to sensitivity and foreground mitigation strategies for EOR observations.

Findings

Measured the dish's angular response at 137 MHz.

Estimated HERA's sensitivity to EOR power spectrum.

Analyzed the impact of beam pattern on foreground distribution in Fourier space.

Abstract

The Hydrogen Epoch of Reionization Array (HERA) is a radio interferometer aiming to detect the power spectrum of 21 cm fluctuations from neutral hydrogen from the Epoch of Reionization (EOR). Drawing on lessons from the Murchison Widefield Array (MWA) and the Precision Array for Probing the Epoch of Reionization (PAPER), HERA is a hexagonal array of large (14 m diameter) dishes with suspended dipole feeds. Not only does the dish determine overall sensitivity, it affects the observed frequency structure of foregrounds in the interferometer. This is the first of a series of four papers characterizing the frequency and angular response of the dish with simulations and measurements. We focus in this paper on the angular response (i.e., power pattern), which sets the relative weighting between sky regions of high and low delay, and thus, apparent source frequency structure. We measure the angular response at 137 MHz using the ORBCOMM beam mapping system of Neben et al. We measure a collecting area of 93 m^2 in the optimal dish/feed configuration, implying HERA-320 should detect the EOR power spectrum at z~9 with a signal-to-noise ratio of 12.7 using a foreground avoidance approach with a single season of observations, and 74.3 using a foreground subtraction approach. Lastly we study the impact of these beam measurements on the distribution of foregrounds in Fourier space.