Using the Sun to Measure the Primary Beam Response of the Canadian Hydrogen Intensity Mapping Experiment

TL;DR

This paper uses the Sun as a natural calibration source to measure the primary beam response of CHIME, covering a large sky area without moving the telescope, and minimizes solar variability effects.

Contribution

It introduces a novel method leveraging the Sun's seasonal motion to calibrate CHIME's beam pattern over a wide sky area.

Findings

Beam pattern covers ~7,200 square degrees

Solar brightness variability is less than 10% during observations

Method complements existing beam measurements

Abstract

We present a beam pattern measurement of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) made using the Sun as a calibration source. As CHIME is a pure drift scan instrument, we rely on the seasonal North-South motion of the Sun to probe the beam at different elevations. This semiannual range in elevation, combined with the radio brightness of the Sun, enables a beam measurement which spans ~7,200 square degrees on the sky without the need to move the telescope. We take advantage of observations made near solar minimum to minimize the impact of solar variability, which is observed to be <10% in intensity over the observation period. The resulting data set is highly complementary to other CHIME beam measurements -- both in terms of angular coverage and systematics -- and plays an important role in the ongoing program to characterize the CHIME primary beam.