Measuring HERA's primary beam in-situ: methodology and first results

TL;DR

This paper develops a novel in-situ method to measure HERA's primary beam using overlapping source tracks, enabling accurate beam characterization crucial for 21cm cosmology, with initial results matching simulations and a new source catalog.

Contribution

It extends existing beam measurement techniques to drift-scan telescopes like HERA, allowing simultaneous source flux and beam response estimation without relying on source catalogs.

Findings

Beam response matches electromagnetic simulations down to -20 dB.

Constructed a catalog of 90 sources at 151 MHz.

Method enables accurate in-situ beam calibration for 21cm cosmology.

Abstract

The central challenge in 21~cm cosmology is isolating the cosmological signal from bright foregrounds. Many separation techniques rely on the accurate knowledge of the sky and the instrumental response, including the antenna primary beam. For drift-scan telescopes such as the Hydrogen Epoch of Reionization Array \citep[HERA, ][]{DeBoer2017} that do not move, primary beam characterization is particularly challenging because standard beam-calibration routines do not apply \citep{Cornwell2005} and current techniques require accurate source catalogs at the telescope resolution. We present an extension of the method from \citet{Pober2012} where they use beam symmetries to create a network of overlapping source tracks that break the degeneracy between source flux density and beam response and allow their simultaneous estimation. We fit the beam response of our instrument using early HERA observations and find that our results agree well with electromagnetic simulations down to a -20~dB level in power relative to peak gain for sources with high signal-to-noise ratio. In addition, we construct a source catalog with 90 sources down to a flux density of 1.4~Jy at 151~MHz.