Characterization of the John A. Galt telescope for radio holography with CHIME

TL;DR

This paper characterizes the John A. Galt telescope's properties to improve radio holography calibration for the CHIME experiment, aiding in precise 21 cm cosmology measurements.

Contribution

It provides detailed analysis of the Galt telescope's system temperature, beam shape, and geometry, enhancing calibration accuracy for CHIME's radio holography.

Findings

Estimated Galt system temperature using drift scans and Haslam map

Determined Galt telescope's beam shape via raster scan of Cassiopeia A

Measured Galt-CHIME geometry for interferometric analysis

Abstract

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) will measure the 21 cm emission of astrophysical neutral hydrogen to probe large scale structure at redshifts z=0.8-2.5. However, detecting the 21 cm signal beneath substantially brighter foregrounds remains a key challenge. Due to the high dynamic range between 21 cm and foreground emission, an exquisite calibration of instrument systematics, notably the telescope beam, is required to successfully filter out the foregrounds. One technique being used to achieve a high fidelity measurement of the CHIME beam is radio holography, wherein signals from each of CHIME's analog inputs are correlated with the signal from a co-located reference antenna, the 26 m John A. Galt telescope, as the 26 m Galt telescope tracks a bright point source transiting over CHIME. In this work we present an analysis of several of the Galt telescope's properties. We employ driftscan measurements of several bright sources, along with background estimates derived from the 408 MHz Haslam map, to estimate the Galt system temperature. To determine the Galt telescope's beam shape, we perform and analyze a raster scan of the bright radio source Cassiopeia A. Finally, we use early holographic measurements to measure the Galt telescope's geometry with respect to CHIME for the holographic analysis of the CHIME and Galt interferometric data set.