Primary Beam Calibration for Commensal Telescopes Utilizing Offset Optics

TL;DR

This paper presents a new calibration method for the VLA Low-band Ionosphere and Transient Experiment (VLITE) that improves primary beam accuracy to within 3%, enabling better brightness measurements in radio astronomy without disrupting primary observations.

Contribution

The study introduces a novel calibration approach using standard candles and beam response models that accounts for offset optics, enhancing calibration precision in commensal radio telescopes.

Findings

Achieved calibration accuracy within 3% across the field of view.

Validated models against holographic methods and light curves.

Enabled reliable measurements under various operational conditions.

Abstract

Accurate primary beam calibration is essential for precise brightness measurements in radio astronomy. The VLA Low-band Ionosphere and Transient Experiment (VLITE) faces challenges in calibration due to the offset Cassegrain optics used in its commensal observing system. This study aims to develop a novel calibration method to improve accuracy with no impact on the Very Large Array (VLA) primary science observations. We used the apparent brightness of standard candles identified in VLITE's commensal data to develop 1D and 2D primary beam response models. These models accounted for operational changes and asymmetries caused by the subreflector and were validated against holographic methods and compact source light curves. The models achieved calibration accuracy within 3 percent across the field of view, significantly improving the precision of brightness measurements. The results were consistent with holography-derived solutions and performed reliably under different operational conditions. This improved calibration technique expands VLITE's capabilities for studying active galactic nuclei, transients, and pulsars. It offers a cost-effective alternative to traditional holographic methods, facilitating broader use in commensal observing systems.