Emil Polisensky ^* Tracy E Clarke Simona Giacintucci Wendy Peters

• Naval Research Laboratory, Washington D.C., United States

Radio astronomy relies on accurate primary beam calibration to achieve precise brightness measurements of astrophysical plasmas across the field of view. This is particularly challenging for commensal observing systems like the VLA Low-band Ionosphere and Transient Experiment (VLITE), operating on the National Radio Astronomy Observatory's Karl G. Jansky Very Large Array (VLA) using offset Cassegrain optics. We present a novel approach for mapping the VLITE primary beam response leveraging the apparent brightness of standard candles identified within VLITE's commensal data. We develop 1D and 2D models that account for the unique beam shapes and asymmetries introduced by the VLA's subreflector and Cassegrain optics.Our technique provides accurate models of the primary beam response for different subreflector positions. We compare our models to those obtained from traditional holographic methods and evaluate their accuracy through calibrated source light curves. The results show that our calibration solutions are accurate to within 3% across the field of view, significantly improving the precision of brightness measurements. The accurate primary beam calibration developed here expands the capabilities of VLITE, enabling broader research in astrophysical plasma studies, including active galactic nuclei, transient phenomena, and pulsars.