L-BASS: a project to produce an absolutely calibrated 1.4 GHz sky map, I -- Scientific rationale and system overview

TL;DR

L-BASS aims to create an absolutely calibrated 21 cm sky map with high radiometric accuracy to improve calibration of higher resolution maps and study the radio background, using a specialized dual-antenna system.

Contribution

This paper introduces the design and scientific rationale of L-BASS, a novel instrument for precise calibration of the 21 cm sky at 1.4 GHz.

Findings

Design achieves <0.1 K calibration accuracy

Dual-antenna system enables independent elevation scanning

Continuous comparison receiver enhances measurement stability

Abstract

L-BASS is an instrument designed to produce an absolutely calibrated map of the sky at a wavelength of 21 cm (L-band) with a radiometric accuracy of less than or equal to 0.1 K and with an angular resolution of 23 degrees. The prime motivations are to improve the temperature calibration of higher resolution maps and to investigate the steep spectrum radio background proposed by the ARCADE 2 team. The instrument consists of a pair of conical horn antennas which can scan independently in elevation; each antenna produces a circularly polarized output. The difference in signals from the antennas is measured with a continuous-comparison receiver connected to a digital spectrometer sampling the signal from 1400 MHz to 1425 MHz within the protected radio astronomy band. We describe the astrophysical motivation for the project, the design requirements and how these will be attained.